a 
 
 Pear 
 
 
 California 
 
 egional 
 
 acility 
 
 --../ x
 
 
 UNIVERSITY OF CALIFORNIA 
 AT LOS ANGELES 
 
 GIFT OF 
 
 Citrus Experiment 
 Rj-.flt.1on
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ENTOMOLOGY BULLETIN No. 118. 
 
 L. O. HOWARD. Entomologist and Chief cf Bureau. 
 
 THE BEAN THRIPS. 
 
 II. M. RUSSELL, 
 
 Entomological Assistant. 
 
 ISSUED OCTOBER 16, 1912. 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING 
 1912.
 
 U. S. DEPARTMENT OF AGRICULTURE, 
 
 BUREAU OF ENTOMOLOGY BULLETIN No. 118. 
 
 L. O. HOWARD. Entomologist and Chief cf Bureau. 
 
 THE BEAN THRIPS. 
 
 H. M. RUSSELL, 
 
 Entomological Assistant. 
 
 ISSUED OCTOHEK 16, 1912. 
 
 WASHINGTON: 
 
 GOVERNMENT PRINTING OFFICE. 
 1912.
 
 BUREAU OF ENTOMOLOGY. 
 
 L. O. HOWARD, Entomologist and Chief of Bureau. 
 
 C. L. MARLATT, Entomologist and Acting Chief in Absence of Chief. 
 
 R. S. CLIFTON, Executive Assistant. 
 
 W. F. TASTET, Chief Clerk. 
 
 F. H. CHITTENDEN, in charge of truck crop and stored, product insect investigations. 
 
 A. D. HOPKINS, in charge of forest insect investigations. 
 
 W. D. HUNTER, in charge of southern fleld crop insect investigations. 
 
 F. M. WEBSTER, in charge of cereal and forage insect investigations. 
 
 A. L. QUAINTANCE, in charge of deciduous fruit insect investigations. 
 
 E. F. PHILLIPS, in charge of bee culture. 
 
 D. M. ROGERS, in charge of preventing spread of moths, fleld ^vork. 
 
 ROLLA P. CURRIE, in charge of editorial work. 
 
 MABEL COLCORD, in charge of library. 
 
 TRUCK CROP AND STORED PRODUCT INSECT INVESTIGATIONS. 
 F. II. CHITTENDEN, in charge. 
 
 H. M. RUSSELL, C. H. POPENOE, WM. B. PARKER, H. O. MARSH, M. H. HIGH, 
 
 FRED A. JOHNSTON, JOHN E. GRAF, entomological assistants. 
 I. J. CONDIT, collaborator in California. 
 W. N. ORD, collaborator in Oregon. 
 THOMAS H. JONES, collaborator in Porto Rico. 
 MARION T. VAN HORN, PAULINE M. JOHNSTON, ANITA M. BALLINGER, prcparators. 
 
 2 
 
 ADDITIONAL COPIES of this publication 
 -A- may be procured from the SUPERINTEND- 
 ENT OF DOCUMENTS, Government Printing 
 Office, Washington, D. C., at 10 cents per copy
 
 a* 
 
 CO 
 
 LETTER OF TRANSMITTAL 
 
 U. S. DEPARTMENT or AGRICULTURE, 
 CQ BUREAU or ENTOMOLOGY, 
 
 Washington, D. C., April 24, 1912. 
 
 SIR : I have the honor to transmit herewith for publication a manu- 
 N script entitled "The Bean Thrips," by H. M. Russell, an entomo- 
 i logical assistant of this bureau. 
 
 v This bulletin deals with an insect pest of the family Thripidae, 
 
 <sJ the study of which has been hitherto largely neglected, and which of 
 
 ^ recent years has attracted considerable attention from an economic 
 
 ^ standpoint, as the cause of immense losses in the Pacific coast regions 
 
 ? and elsewhere to truck farmers. The insect is closely related to the 
 
 \ tobacco thrips, as well as to the onion thrips, to which species are 
 
 t chargeable untold losses in the production of these two staples. Ex- 
 
 4 periments to produce formulae and devices with which successfully 
 
 Nj^to combat this insect are being perfected, and methods for the com- 
 
 As plete control of the pest are early expected. 
 
 I recommend the publication of this manuscript as Bulletin No. 
 (118 of this bureau. 
 
 Respectfully, L. O. HOWARD, 
 
 Chief of Bureau. 
 Hon. JAMES WILSON, 
 
 Secretary of Agriculture. 
 
 3 
 
 243602
 
 CONTENTS. 
 
 Page. 
 
 Introduction 7 
 
 Nature and extent of injury 8 
 
 Description 8 
 
 The adult female 9 
 
 The adult male 10 
 
 Recently emerged adults 10 
 
 The egg 10 
 
 The first-stage larva 10 
 
 The second-stage larva 11 
 
 The young nymph or prepupa 12 
 
 The full-grown nymph or pupa 13 
 
 Origin and distribution 14 
 
 History 16 
 
 Recent records 16 
 
 Habits of the adult 17 
 
 Method of mating 17 
 
 Method and time of oviposition 18 
 
 Number of eggs and period of oviposition 19 
 
 Proportion of the sexes 20 
 
 Kinds of reproduction 20 
 
 Feeding habits 20 
 
 Flight 21 
 
 Leaping 22 
 
 Normal length of life 22 
 
 Length of life in winter 22 
 
 Habits of the larva 23 
 
 Hatching 23 
 
 Molting 25 
 
 Habits of the prepupa and pupa 26 
 
 Food plants 27 
 
 Beans 27 
 
 Other vegetables 28 
 
 Pear 28 
 
 Alfalfa 28 
 
 Cotton 30 
 
 Wild plants 30 
 
 Seasonal history at Compton, Cal 31 
 
 The egg. , 31 
 
 The larva 32 
 
 The prepupa and pupa 34 
 
 Total life cycle 36 
 
 Emergence from hibernation 36 
 
 Entrance into hibernation 36 
 
 Number of generations 37 
 
 5
 
 THE BEAN THKIPP. 
 
 Page. 
 
 Seasonal history in the Imperial Valley 37 
 
 Egg period 37 
 
 Larval period 38 
 
 Prepupal and pupal periods 38 
 
 Seasonal history at Tempe, Ariz 33 
 
 Hibernation 39 
 
 Notes on occurrence 40 
 
 Natural control 40 
 
 Rains 40 
 
 Natural enemies 41 
 
 Artificial control 42 
 
 Cultural methods 42 
 
 Spraying 43 
 
 Distributing the parasites 44 
 
 Bibliography 44 
 
 Index... 47 
 
 ILLUSTRATIONS. 
 
 Page. 
 
 FIG. 1. Side view of the head of a thrips, showing the mouthparts 8 
 
 2. The bean thrips (Heliothrips fasciatus) : Adult female and details 9 
 
 3. The bean thrips: Eggs 10 
 
 4. The bean thrips: First-stage larva 11 
 
 5. The bean thrips: Second-stage larva 12 
 
 6. The bean thrips: Prepupa 12 
 
 7. The bean thrips: Pupa 13 
 
 8. Map showing present known distribution of the bean thrips (Heliothrips 
 
 fasciatus) 15 
 
 9. Alfalfa showing injury by the bean thrips 29 
 
 10. The bean thrips: Prepupse parasitized by Thripoctenus russelli 41 
 
 11 . A hymenopterous parasite, Thripoctenus russelli: Adult 42
 
 THE BEAN THRIPS. 
 
 (Heliothrips fasciatus Pergande.) 
 
 INTRODUCTION. 
 
 In the State of California during the past four or five years the 
 bean thrips has been reported with increasing frequency as a serious 
 pest to various crops. The common name " bean thrips " is somewhat 
 of a misnomer, as this insect feeds on many different crops, but is re- 
 tained here, as it is well known by that name in California. That 
 State, with its long, dry summer, furnishes climatic conditions un- 
 usually favorable to the development of thrips, and several species 
 have gained such a foothold there as annually to cause a loss of hun- 
 dreds of thousands of dollars. 
 
 In the summer of 1909, Mr. R. S. Woglum, of the Bureau of En- 
 tomology, informed the author that during the summer before he had 
 seen hundreds of acres of beans in southern California so seriously 
 infested by the bean thrips that they had the appearance of plants 
 scorched by fire; and as this thrips seemed to be increasing in num- 
 bers and destructiveness it appeared to be the part of wisdom to 
 obtain all possible information concerning its life history and control 
 before it reached the enormous abundance of the destructive pear 
 thrips (Eutkrips pyri Daniel). When, therefore, the Bureau of 
 Entomology established a field station at Compton, Cal., in Septem- 
 ber, 1909, for the study of truck-crop ard sugar-beet insects, the 
 writer planned, among other projects, to undertake as complete a 
 study of this insect as time would permit. With this in mind, the 
 bean thrips has been the subject of thorough investigation during the 
 years 1910 and 1911. During this time, however, the insect was not 
 again so destructive to beans, so that remedies with spray mixtures 
 could not be thoroughly tested. Nevertheless, as the life history has 
 been worked out and a large fund of information obtained on the dis- 
 tribution and habits of this thrips, together with knowledge of a 
 natural enemy of some promise, this paper is published at the present 
 time. 
 
 At Compton, in Los Angeles County, where the life history of this 
 insect was studied by the writer, the temperature is quite cool, since 
 the location is near the coast. 
 
 7
 
 8 THE BEAN THRIPS. 
 
 In the Imperial Valley the life history of the bean thrips and its 
 injuries to alfalfa and cotton have been investigated by Mr. V. L. 
 Wildermuth, of this bureau, and where his observations are used 
 credit is given in the text. 1 Use has been made of observations, 
 by Messrs. P. R. Jones and S. W. Foster, of this bureau, on this insect 
 in the more northern points in the State. Since July, 1911. the writer 
 has been ably assisted by Mr. John E. Graf. He also wishes to ex- 
 press his appreciation to Dr. F. II. Chittenden, under whose direc- 
 tions he has conducted the investigation, and to Prof. F. M. Webster 
 for the free use of notes obtained by his agents. 
 
 NATURE AND EXTENT OF INJURY. 
 
 The damage caused by the bean thrips is not confined to the foliage, 
 but affects as well the fruit and stems of the plant attacked. The 
 injury is caused by the method of feeding. 
 Both young and adults obtain their food by 
 puncturing the leaf tissue with their sharp 
 mouthparts and, after lacerating it, with- 
 drawing the plant juices at the point of 
 attack. Figure 1, although a drawing of a 
 different species, gives an idea of the mouth- 
 parts of this insect. 
 
 Each time as the contents of the leaf at 
 the point attacked are removed, the thrips 
 moves to a new point and repeats the opera- 
 tion, so that if the insects are abundant or 
 the attack is long continued the leaf tissue is 
 showing destroyed over the entire surface. As the 
 the mouthparts: Much en- sll pplv O n one side of the leaf is exhausted 
 
 larged. (After Moulton.) * \ " . , 
 
 the larva? move around to the other, or if 
 
 adults are present these fly or jump to more tender leaves. The 
 infested and badly injured leaves turn yellowish or white, dry up, 
 and either drop off or hang lifeless to the plant. Then, as the 
 attack continues, successive leaves are attacked until in extreme 
 cases the entire plant is killed. 
 
 DESCRIPTION. 
 
 Heliothrips fasciatus belongs to the Suborder Terebrantia and the 
 Family Thripida? of the Order Thysanoptera, being placed in this 
 position 15ecause of the downward-curved ovipositor of the female. 
 The 8-segmented antenna?, with the last segment much longer than 
 the Tth, and the reticulated surface of the body, together with the 
 pointed spines on the wings, place this insect in the Genus Helio- 
 
 *Mr. Wildermuth studied the insect in its relation to alfalfa, without knowing that It 
 was being investigated by the author. His studies, made under quite different climatic 
 conditions, add materially to the value of the results obtained.
 
 DESCRIPTION. 
 
 9 
 
 thrips. The habits of the larva are also quite characteristic of this 
 genus, for the habits of the larvae of the greenhouse thrips (Helio- 
 //<///>* hvemorrhoidalis Bouche) and of Heliothrips rubrodnctus 
 Giard are almost identical with those of the present species. 
 
 THE ADULT FEMALE. 
 
 The adult female (fig. 2) is about one-twenty-fourth of an inch 
 in length (0.9815 mm. to 1.1174 mm.; average, 1.0405 mm.) and 
 about one-fourth as wide as long (0.2265 mm. to 0.2869 mm.; average 
 
 Via. 2. The bean thrips (Ueliothnps fasciatm) : a, Adult female ; 6, ventral side of 
 abdominal segment of same; c, antenna of same, a, Greatly enlarged; 6, c, more 
 enlarged. ^(Original.) 
 
 width, 0.2529 mm.) and is fusiform in shape. The head and body 
 are black and, under the microscope, are seen to be covered with 
 distinct reticulations and short white hairs. The antennae are 8- 
 segmented and two and one-half times as long as the head, and are 
 held out in front of the body. They are black, more or less banded 
 with white, and bear white hairs. The wings are held folded to- 
 gether down the middle of the dorsum; they are black, crossed by 
 a white band at the base and a white band at three-fourths the dis- 
 tance from the base. The wings are fringed with long white hairs. 
 The legs are black, banded with white. 1 
 
 1 For a detailed description of tho genus and the- species for use of systematists, S-P 
 Hinds's "Monograph of the Thysanoptera " (Proc. U. S. Nat. Mus., vol. 26, 1902), pp. 
 174-175. 
 
 51097 Bull. 11812 2
 
 10 THE BEAN THKIPS. 
 
 THE ADULT MALE. 
 
 The male resembles to a great extent the female, as the color 
 and the markings are the same, but it is noticeably smaller in size 
 and apparently more active. When viewed under the microscope 
 the sexual organs are seen to be distinctly different, and in light- 
 colored or cleared specimens the testes may be seen as two orange-red 
 bodies in the abdomen, and on the middle of each of segments 2 to 6 
 on the ventral side are yellowish oval spots. The total length of 
 the male is 0.7097 mm. to 0.8002 mm. ; the average, 0.7474 mm. The 
 greatest width across the mesothorax is 0.1963 mm. to 0.2114 mm. ; 
 the average, 0.1978 mm. 
 
 RECENTLY EMERGED ADULTS. 
 
 Both sexes, when just emerged, have the head and thorax a light 
 yellowish orange, with the eyes and ocelli bright red. The antennrc 
 are white and ringed with brown, while the wings are dusky, crossed 
 by bands of a darker color. The legs are 
 white, with ends of each segment more or less 
 black. Gradually the color darkens, and in 
 a day they all have the fully matured colors, 
 as described above. 
 
 FIG. 3. The bean thrips : The egg (fig. 3) is bean shaped, 0.21 to 
 enlarged ' 0.255 mm. in length and 0.105 to 0.12 mm. in 
 width, and is very delicate and thin shelled. 
 It is translucent white, with a smooth shining surface. The eggs are 
 laid in the tissue of the leaf or in the veins, or even in the stems, and 
 in case of beans may be laid in the pods themselves. As the embryo 
 within develops, the egg becomes swollen, and the little pocket in 
 which it is inserted becomes raised above the leaf surface. The eggs 
 may be seen in the leaf tissue if examined with a hand lens before 
 the light. Each little egg pocket stands out, because of its lighter 
 color, and within the crude outline of the egg may be seen. 
 
 The younger stages of this insect differ distinctly from those of 
 Heliothrips hcemorrhoidalis * in the dashes of crimson so generally 
 present on the sides. 
 
 THE FIRST-STAGE LARVA. 2 
 (Fig. 4.) 
 
 Length, 0.42 mm. ; width" of mesothorax, 0.135 mm. General shape fusiform, 
 similar to Heliothrips hcemorrhoidalis; head, antennae, and legs large in propor- 
 
 1 For description of Hcliotlirips hcemorrhoidalis, see " The Greenhouse Thrips," Bui. 64, 
 Part VI, Bur. Ent., U. S. Dept. Agr., pp. 46-48, 1909. 
 
 Description made while larva was very young and before feeding commenced.
 
 DESCRIPTION. 
 
 11 
 
 tiou to rest of the body. Color traiisJuceut white. Head large, quadrate; eyes 
 reddish ; ocelli absent. Antennae 0.195 mm. in length, apparently 7-segmented ; 
 basal segment cylindrical, short; second nearly twice as long as first, barrel- 
 shaped; third and fourth spindle-shaped, ringed with a few fine hairs; fifth, 
 sixth, and seventh slender, nearly equal in length. Legs translucent white. 
 Abdomen tapering posteriorly ; first eight segments nearly equal in length, last 
 two segments longer than others ; each abdominal segment with longitudinal 
 rows of setae, the tenth with 
 four setae about 0.045 mm. in 
 length. 
 
 At this stage there seems to 
 be nothing to distinguish this 
 species from H. hoemorrhoidalis. 
 
 THE SECOND-STAGE LARVA. 
 (Fig. 5.) 
 
 Length. 1.05 mm. ; width of 
 mesothorax, 0.27 mm. Shape 
 fusiform, about same as larva ; 
 of mesothorax and meta thorax 
 long, robust, cylindrical; sides 
 of mesothorax and metathorax 
 and first five abdominal seg- 
 ments nearly parallel ; pro- 
 thorax narrowed toward head ; 
 last five abdominal segments 
 tapering to the last segment, 
 which is cylindrical and trun- 
 cated at end. Color of head 
 and pro thorax light yellow, 
 mesothorax and metathorax 
 and first six segments of abdo- 
 men translucent white, stained 
 on sides with crimson blotches 
 and with yellow on dorsum to 
 some extent; next three seg- 
 ments of abdomen the color of 
 head, last segment of abdomen 
 white; alimentary tract plainly 
 indicated by the brownish color 
 given it by inclosed food. Surface of body covered with minute granulations. 
 Head quadrate, rounded in front and notched behind the eyes, 0.12 mm. long, 
 O.OS25 mm. wide ; eyes small, reddish ; ocelli absent. Antennae 7-segmented, first 
 four segments the color of head, the others translucent- white; first segment 
 short, cylindrical; second longer, barrel-shaped; third and fourth spindle-shaped 
 'and annulated; fifth, sixth, and seventh slender and cylindrical. Legs long, 
 yellowish. Abdomen 0.60 mm. in length, fusiform, ovipositor not formed; seg- 
 ments with rows of fine setu^ increasing in length toward posterior end; ninth 
 and tenth segments with longer setae. 
 
 FIG. 4. The bean thrips : First-stage larva. Greatly 
 enlarged. (Original.)
 
 12 
 
 THE BEAN THKIPS. 
 
 THE YOUNG NYMPH OR PREPUPA. 
 (Fig. 6.) 
 
 Length, 1.02 ram.; width of mesothorax, 0.255 mm. Shape fusiform, similar 
 to adult. Head, length, 0.09 mm. ; width at eyes, 0.157 mm. Head translucent 
 white, vertex slightly yellowish, ocelli absent. Head rounded in front, slightly 
 notched behind the eyes; eyes red, made up of a few facets, surface faintly 
 reticulated ; two pairs of setse behind the eyes and two pairs between the eyes. 
 Antennae translucent white, extending forward, 0.195 mm. in length; segments 
 indistinct but apparently 7-segmented. 
 
 Prothorax about one-half again as wide as long, sides rounded, posterior edge 
 broadest, semitranslucent white to yellow, posterior angles tinted with crimson. 
 
 PIG. 5. The bean thrips : Second- 
 stage larva. Greatly enlarged. 
 (Original.) 
 
 FIG. 6. The bean thrips: Prepupa. 
 Greatly enlarged. (Original.) 
 
 setae around margin. Mesothorax with rounded angles, translucent white to 
 faint yellow, sides and posterior angles tinted with crimson, wing-cases trans- ^ 
 parent white, distinct from each other, those of forewings extending to middle 
 of second abdominal segment and those of hind wings extending to middle of 
 third abdominal segment. Legs strong, translucent white. 
 
 Abdomen fusiform as in adult, translucent white to faint yellowish, edges 
 with tint of crimson, which enlarges to fair-sized blotches on sides of seventh 
 and eighth segments; number of longitudinal rows of setse increasing in length 
 toward posterior end. Length of abdomen, 0.62 mm.
 
 DESCRIPTION. 
 THE PULL-GROWN NYMPH OR PUPA. 
 
 13 
 
 (Fig. 7.) 
 
 Length, 0.99-1.09 mm. ; width at mesothoracic angles, 0.24-0.255 mm Shape 
 similar to that of adult. Color orange; posterior border of prothorax 
 mesothoracic angles, sides, and abdominal segments 2, 3, 6, and 7 more or less 
 crimson. Head, length, 0.11 mm. ; width, 0.18 mm. ; orange, apparently faintly 
 reticulated ; eyes dark red, larger than in prepupal stage, facets small. Three 
 ocelli present in close triangle between eyes, in color yellow. Antenna* laid 
 backward on head and reaching to beyond middle of prothorax ; segments in- 
 distinct, translucent white; 
 segments 1 and 2 projecting 
 in front of the head and 2 
 with four setae or hairs, two 
 extending forward, about 
 0.0135 mm. in length. Tho- 
 rax light orange or yellow. 
 Prothorax about twice as 
 wide as long. Wing-cases 
 0.54 mm. long, extending to 
 seventh abdominal segment, 
 translucent white. Length 
 from head to end of wing- 
 pads, 0.825 mm. Legs trans- 
 lucent white. Abdomen 
 fusiform, similar to adult, 
 surface plainly reticulated 
 in older specimens, seta? 
 well developed, the longest 
 ones at posterior end. 
 Length of abdomen, 
 mm. ; width, 0.31 
 length of posterior 
 O.OS5 mm. 
 
 The younger stages of this 
 insect differ distinctly from 
 those of 11. hcemorrhoidaUs* 
 in the dashes of crimson so 
 generally present on the 
 sides. 
 
 The pupa of the male 
 is shorter and more slen- 
 
 0.612 
 mm. ; 
 seta?, 
 
 PIG. 7. The 
 
 Greatly enlarged. 
 
 der than that of the fe- 
 male. This pupa differs 
 from H. hcemorrhoidalis in its smaller size, in its yellow color, with 
 the sides of the abdomen more or less stained with crimson, and in 
 having the hairs of the body longer and the second segment of the 
 antennae with two long setae. 
 
 The foregoing descriptions are for the parts of California in Los 
 Angeles County and more northern points, for Mr. Wildermuth 
 
 1 For description of Heliothrips fuemorrhoidrilis, see " The Greenhouse Thrips," Bui. 04. 
 Part VI, Bur. Ent., U. S. Dept. Agr., pp. 46-48. 1909.
 
 14 THE BEAN THRIPS. 
 
 found that the different stages in the Imperial Valley lacked the red 
 markings except in the cooler weather of the late fall. 
 
 ORIGIN AND DISTRIBUTION. 
 
 This insect was first described by Mr. Theodore Pergande from 
 specimens taken in Yuba County, Cal. A few years later he identi- 
 fied a thrips from Lewiston, Idaho, as this same species. 
 
 Mr. Dudley Moulton reported that this species had been collected 
 in Colusa County by Mr. E. K. Carnes, in Santa Rosa County by 
 Mr. O. E. Bremner, and in the Santa Cruz Mountains, Santa Clara 
 County, by himself. Mr. D. L. Crawford recorded fasciatus from 
 Santa Paula, Ventura County, Cal., and from Claremont arid Chino, 
 Cal. Mr. William B. Parker, of this bureau, collected it at Davis and 
 Hamilton City, Cal. Mr. P. R. Jones, engaged in pear thrips in- 
 vestigations, reports that this insect occurs very commonly around 
 Lindsay and San Jose, Cal. Mr. S. W. Foster, while engaged in the 
 same investigation, collected this insect from Martinez, Cal., and later 
 found it " frequently throughout Contra Costa County." 
 
 Mr. V. L. Wildermuth, engaged in cereal and forage insect in- 
 vestigations, has collected this insect in California at Indio, River- 
 side County, and at Bard, El Centre, and Holtville, Imperial County, 
 and in Arizona at Yuma, Yuma County, Buckeye and Tempe, Mari- 
 copa County, and Sacaton, Pinal County. 
 
 During the present investigation the writer has collected this insect 
 quite extensively from many places in southern California. In 1910 
 it was found to be very abundant on wild lettuce in several yards 
 and alleys in the city of Los Angeles itself. At various times it 
 has been collected from Bell, Compton, Gardena, Glendale, Holly- 
 wood, Laurel Canyon, Puente, San Gabriel, Sierra Madre, Tropico, 
 and Whittier, in Los Angeles County. In Laurel Canyon the author 
 found it feeding on wild food plants in uncleared land about 6 miles 
 from cultivated fields. It was also collected near the entrance of the 
 canyon, scattered over the mountain sides on various wild plants. At 
 Sierra Madre it was taken at an elevation of 750 feet. 
 
 It was also collected at Garden Grove, Huntington Beach, Smelt- 
 zer, and Sunset Beach, in Orange County, Cal. While on a trip in 
 October, 1910, the author found this insect to be generally distributed 
 throughout the town of Oxnard, and in Mental vo and the entire 
 outlying sugar-beet district of Ventura County. 
 
 In February, 1911, the author made a trip to San Diego to investi- 
 gate the conditions in reference to truck crops there, and in Mission 
 Valley a long, narrow, and fertile valley lying to the north of San 
 Diego, and devoted to truck crops this insect was found feeding to 
 some extent on pea vines. The writer left California for Washing- 
 ton, D. C., in September, 1911, and while delayed at Sparks, Nev., 
 he examined several clumps of wild lettuce growing along the rail-
 
 ORIGIN AND DISTRIBUTION. jg 
 
 road track and collected both larval and adult forms of th, I,,,,,, 
 thnps upon this plant. 
 
 tl ^ A i; *' ^iT^'f thiS bUreaU ' reC6ntly re P rted to the wri *er 
 that he had collected the species on October 10, 1910, at Clarksville. 
 
 *T'r7 thlS mS6Ct is S0 widel y distributed in all parts 
 
 of California seems to point strongly to that State as its original 
 home. This is also strongly supported by the fact that Moulton 
 collected it from wild vetch in the Santa Cruz Mountains and that 
 the writer collected it in wild, uncultivated tracts in the mountains 
 and canyons north of Los Angeles, 5 and 6 miles from cultivated 
 crops. This point of view is further strengthened, because the au- 
 thor has found this insect feeding on more than 20 native wild 
 plants. 
 
 FIG. 8. Map showing present known distribution of the bean thrips (Ilelio1hrii>x }iiK,-iiHux\. 
 
 (Original.) 
 
 Mr. J. D. Hood, formerly of the office of the State entomologist 
 of Illinois, recently informed the writer that he possessed specimens 
 of this thrips that were collected by Prof. Lawrence Bruner at 
 Lincoln, Nebr., February 14, 1899, and that he had collected this 
 same species at Urbana, 111., in March, 1907. In both cases the 
 thrips were taken on California oranges and had evidently been cur- 
 ried across the country while hibernating in the navel end of the 
 fruit. This is an excellent illustration of how this insect may be 
 distributed through the agency of man. 
 
 Although this insect is quite minute and has been little studied, 
 at the present time it is known to occur through the entire State of 
 California, in several places in Arizona, in Nevada, and in Idaho 
 near the Washington State line. It has also been found in one 
 locality in Tennessee. Figure 8 has been prepared to show the 
 present definite localities where this insect has been observed.
 
 16 THE BEAN THRIPS. 
 
 Without doubt this insect occurs over the entire Pacific coast of 
 the United States and down into Mexico for some distance and pos- 
 sibly even into Central America. As it becomes better known it 
 will probably be found to occur in several of the other Western 
 States and some of the Eastern States as well. 
 
 HISTORY. 
 
 In 1895 Mr. Theodore Pergande (I) 1 described this species from one 
 specimen received from Yuba County, Cal., where it was taken on 
 an orange leaf infested with (Aspidiotus} Chrysomphalus aurantii 
 Mask. At that time he expressed the opinion that the occurrence 
 on this plant was accidental. In view of our present knowledge, 
 however, of the feeding habits of this insect, this specimen was 
 probably feeding on the foliage of the orange itself. 
 
 In 1902 Hinds (3) redescribed the female from one specimen in 
 the collection of the Bureau of Entomology. At that time he wrote 
 that nothing was known of the life history. 
 
 Miss Daniels (4), writing in 1904, noted the occurrence of this 
 thrips in California. At the same time she erected a new genus and 
 species, Caliothrips woodworthi (4), for the male of Heliothrips 
 fasciatus. This error was first pointed out by Dudley Moulton (6) 
 in 1907, and the present writer agrees with him, as the male of 
 fasciatus fits the description exactly except in the number of. an- 
 tenna 1 segments. Undoubtedly Miss Daniels made a mistake in the 
 number of segments in the antenna, since fasciatus is 8-segmented only. 
 
 Crawford (7), in 1909, under "Notes on California Thysanop- 
 tera," records taking numerous specimens in southern California. 
 These were captured on pine, Lotus glaber, and apple. 
 
 Under the name Euthrips fasciatus, Bremner (8), in 1910, reported 
 this insect as injuring beans and peas and as occurring on alfalfa 
 and on peach and pear trees. He recommended spraying with nico- 
 tine solutions, and wrote that of these sulphate of nicotine in the 
 proportion of 1 ounce to 5 gallons of water had given perfect 
 success. 
 
 In 1911 Coit and Packard (9) wrote that the bean thrips caused 
 considerable defoliation to cotton and alfalfa in Imperial Valley, Cal. 
 Moulton (10) also gave a list of its food plants. 
 
 The present writer, in 1911 (12) and also in 1912 (13), published 
 two papers dealing with the life history and habits of Thripoctenus 
 russelli Crawf., a parasite reared in large numbers from this thrips. 
 
 RECENT RECORDS. 
 
 This species, as identified by Mr. Pergande, was sent to the Bureau 
 of Entomology January 25, 1898, by Mr. M. J. Wessels, of Lewiston, 
 
 1 Numbers in parentheses refer to the Bibliography, pp. 44-45.
 
 HABITS OF THE ADULT. J^ 
 
 Idaho, who collected it in a diseased spot of a crab apple. On Augi^t 
 27, 1908, Mr. I. J. Condit sent in specimens of this thrips from 
 Davis, Cal., where they were injuring sugar beets. He wrote: 
 
 I examined the beets and found them literally covered with thrips both tlu- 
 surface and underside of the leaves being badly infested. There were very 
 few leaves which were not attacked, most of them having the appearance of 
 the specimens sent. A field of tomatoes near by was also becoming infested 
 The lower leaves especially were yellow and some falling off. 
 
 Mr. S. W. Foster informed the writer that on August 26, 1900, 
 Mr. Frank T. Swett, of Martinez, Cal., sent to the laboratory of 
 the Bureau of Entomology at Walnut Creek, Cal.. a quantity of 
 pear leaves badly injured by this species. On August 31 Mr. Foster 
 visited the orchard and found the injury quite noticeable. He wrote 
 that " the foliage gave the appearance from a distance of having 
 been scalded." Mr. V. L. Wildermuth, of this bureau, sent speci- 
 mens taken on alfalfa at Indio, Cal., on July 2, 1910. Mr. A. 
 McLachlan, of Davis, Cal., sent in specimens of this thrips on 
 October 13, 1910, with the report that they were injuring the buds 
 and tips of cotton. 
 
 Mr. W. B. Parker, of this bureau, under date of August 25, 1911, 
 sent this insect from Davis, Cal., with the statement that it was 
 causing serious damage to the foilage of the sugar beet. He also 
 collected it on sugar beets at Hamilton City, Cal., on September 18, 
 1911, where it was causing some injury. He wrote, however, that 
 owing to the lateness of the season when the beets were attacked 
 probably only slight damage resulted. 
 
 HABITS OF THE ADULT. 
 
 For a short time after emerging from the pupa this insect remains 
 quiet and appears to be waiting for its limbs to harden. During 
 this time the colors, which were light at emergence, gradually darken. 
 After hardening the thrips moves off and begins feeding. 
 
 METHOD OF MATING. 
 
 The males and females of this species seem to emerge from the 
 pupa at about the same time. During this investigation it was ob- 
 served that, under laboratory conditions at least, the sexes mated 
 generally in from two to three days after emergence and in some 
 cases in even less time. This operation has been observed both in 
 the field and in the laboratory and was identical under both condi- 
 tions. This is probably best described by the original field notes 
 made at the time of observation. 
 
 51097 Bull. 11812 3
 
 18 THE BEAN THKIPS. 
 
 The male, 1 when inclined to copulate, picks out a female, and if 
 she is moving over the leaf runs after her and jumps or alights on her 
 back. In some cases he then spreads the wings and moves them up 
 and down, at the same time moving the tip of the abdomen in the 
 same manner. In other cases the male, after leaping onto the back 
 of the female, remains motionless for some time in that position. It 
 then exserts the copulatory organs from the tip of the abdomen and 
 shifts around toward the side of the female, at the same time bend- 
 ing the abdomen under to the ventral side of that of the female. The 
 copulating organs are then moved back and forth until they en- 
 counter those of the female. In some cases observed, when the male 
 did not succeed in connection, it would withdraw to its former posi- 
 tion on the female and after remaining quiet for a short time would 
 move over and attempt the act on the opposite side. As soon as con- 
 nection is made the male remains motionless for a short time, during 
 which period the female, in many cases, craAvls slowly around on 
 the leaf. After a few minutes the male relinquishes his hold with 
 the copulating organs and moves squarely back onto the dorsum of 
 the female. Soon after the male crawls off and away from the female. 
 This entire operation was observed in three cases to occupy 3, 5, and 
 10 minutes. Several cases were observed where two males attempted 
 copulation with the same female, but, after a vain attempt, one 
 general!} 7 left her. 
 
 METHOD AND TIME OF OVIPOSITION. 
 
 Exactly how much time elapses between copulation and oviposition 
 was not observed, but probably not more than a day, so that the 
 female will begin oviposition within three days from the time she 
 emerges from the pupa. In one case adults emerged on July 19, 
 1911, and eggs were laid four days later. 
 
 Oviposition usually takes place during the night, but has been 
 observed at 2, 3, and 4.30 in the afternoon. A female engaged in 
 oviposition was observed to crawl over the leaf of the food plant 
 for a short distance and then to stop and scrape a hole in the leaf 
 with her mouth cone. This was accomplished by a slight forward 
 and backward motion like that of a chisel. In a short time the 
 female ceased this action and moving forward until she could place 
 the tip of the abdomen where the tissue had been ruptured, arched 
 the abdomen in the middle, arid brought the tip to the opening in 
 
 1 Pietro Buffa (Atti Soc. Toscano Soc. Nat. Mem., vol. 23, p. 48, 1907) figures JEolothrips 
 fasciatus, female and male in copulation, in a position identical with that observed by 
 the writer in Heliothrips fasciatus on many different occasions. 
 
 A. F. Shull (A Biological Survey of the Sand Dune Region of Saginaw Bay, Mich., 
 pp. 190-192), describing copulation in the suborder Terebrantia, expresses doubt as to 
 the position of the male on the back of the female during copulation. As his observa- 
 tions on Euthrips tritici were made under unfavorable conditions his conclusions were 
 probably erroneous.
 
 HABITS OF THE ADULT. 
 
 19 
 
 the leaf surface. She then proceeded to work the ovipositor back 
 and forth in the rupture until she had made an incision of sufficient 
 depth. After this she became motionless for a varying lenih of 
 time, while the egg was being deposited, whereupon the ovipositor 
 was removed, and the female moved away. 
 
 A number of cases have been observed where the female after 
 inserting the ovipositor, could not withdraw it, and, thus held, she 
 soon died. 
 
 NUMBER 01* EGGS AND PERIOD OF OVIPOSITION. 
 
 Owing to the artificial means used in studying the habits of this 
 insect it was impossible to determine exactly how many eggs a 
 female is capable of laying. However, the writer confined T fe- 
 males in a vial for observation. They laid an average of 35.5 egg 
 each, while the highest average for any day was 5.5 eggs each. 
 Another female, during the period from August 16 to August 23, 
 1911, laid 16 eggs, the greatest number laid in any one day being 5. 
 At Compton, Cal., during 1911, females kept in confinement were 
 observed to oviposit for 30 days in succession, while others were 
 observed to oviposit 51 and 83 days after they emerged from the 
 pupae. If this insect normally continues oviposition regularly over 
 a period of 83 days the total number of eggs laid must be very large. 
 
 Mr. V. L. Wildermuth, while in the Imperial Valley, made some 
 interesting notes on the number of eggs this species may deposit. 
 On August 2, 1910, he confined 2 females on leaves of alfalfa in 
 a vial, and on August 5 these leaves contained 50 eggs, or an average 
 of 25 eggs each in 3 days. His other observations are given in 
 Table I. 
 
 TABLE I. Number of eggs deposited by the bean thrifts (Hcliothriiis Jasciatus), 
 Imperial Valley, Cal., 1910. 
 
 Ejtper- 
 iment 
 No. 
 
 Date female 
 was put in vial. 
 
 Date and number of eggs. 
 
 Total 
 period of 
 oviposi- 
 tion. 
 
 Total 
 number 
 of eggs. 
 
 1910. 
 
 Eggs. 
 
 1910. 
 
 Eggs. 
 
 1910. 
 
 Eggs. 
 
 Dead. 
 
 1 
 2 
 3 
 4 
 
 5 
 
 1910. 
 Aug. 29 
 Aug. 31 
 do 
 do 
 
 1911. 
 Sept. 28 i 
 
 Sept. 1 
 Sept. 4 
 Sept. 7 
 Sept. 1 
 
 Sept. 30 
 
 36 
 42 
 53 
 20 
 
 12 
 
 Sept. 2 
 
 6 
 
 Sept. 6 
 
 37 
 
 1 
 
 **-, 
 
 3 
 6 
 
 1 
 
 46 
 
 79 
 42 
 53 
 30 
 
 134 
 
 Oct. 3 
 Oct. 6\ 
 Nov. 1 
 
 25 
 
 47 
 27 
 
 Oct. 11 
 'Nov.'ii" 
 
 24 
 .... 
 
 Record made at Tempe, Ariz. 
 
 Iii these experiments the longest period of oviposition was 46 days, 
 and the largest number of eggs laid by a single female, 134. 
 
 It will be observed from these figures that the females observed by 
 Mr. Wildermuth deposited more eggs and at a more rapid daily rate
 
 20 THE BEAN THRIPS. 
 
 than those observed by the writer. This may have been due to the 
 higher temperature of the Imperial Valley and vicinity, where his 
 observations were made. Mr. Wildermuth noted adults in copula- 
 tion the day that they emerged, and oviposition on the following 
 date. He also observed this species to oviposit during the entire day, 
 whereas the writer never observed it to oviposit except in the after- 
 noon or night. 
 
 PROPORTION OF THE SEXES. 
 
 The bean thrips was under the observation of the writer for a 
 period of more than two years, during which time it had been ob- 
 served in the field at all times of the year. In all observations made 
 during the investigation of this insect the males and females were 
 collected together and copulation was observed from early in Febru- 
 ary until reproduction ceased late in the fall. Apparently the 
 females outnumber the males, but this may be due to the fact that 
 the females are not quite so active as the males, and are not dis- 
 turbed on the plants when examined. On June 9, 1911, out of 17 
 specimens reared in the laboratory 9 were females and 8 males. July 
 17, 1911, the writer examined another series of live adults that were 
 reared in the laboratory. Out of 10G, 80 were females and 2G males. 
 A third series of reared adults was examined October 16, 1911, and 
 out of 4A adults 32 were females and 12 males. Apparently the per- 
 centage of females is too high and does not indicate the exact rela- 
 tion between the sexes. 
 
 KINDS OF REPRODUCTION. 
 
 In all observations made on this topic reproduction has been 
 bisexual, and in view of the fact that males were observed at all 
 times and copulation also occurred at all times in the year when 
 this insect was active, this would seem to be the usual method. How- 
 ever, although the few experiments made to determine whether 
 parthenogenesis occurred gave negative results, in view of the pre- 
 ponderance of females during certain parts of the season it is quite 
 probable that asexual reproduction may occur. It would seem that 
 this method would occur under certain conditions, especially in 
 view of the fact that the greenhouse thrips (Heliothrips hamorrhoi- 
 dalis) 1 reproduces, so far as we know., asexually only, the male hav- 
 ing never been discovered. 
 
 FEEDING HABITS. 
 
 Both the adult and larva of this thrips injure the host by feeding 
 on the foliage. As in the case of the greenhouse thrips, the lower 
 
 1 " The Greenhouse Thrips," Bui. 64, Bur. Ent., U. S. Dept. Agr.
 
 HABITS OF THE ADULT. 21 
 
 and earlier leaves are first attacked in the spring by the adults. 
 These feed on the underside of the leaves, scraping out the leaf 
 content in small spots that become white and conspicuous. Often 
 the adults move along and leave a chain of white spots to mark their 
 progress. The adults also feed to some extent on the surface. 
 As they feed the females deposit their eggs in the leaf tissues, and 
 as soon as incubation is completed the larva? hatch and join the 
 adults on the leaves. Under these conditions the leaves become more 
 or less dried and lifeless, and the adults move to the higher and more 
 tender leaves of the plant. In this way the entire plant may become 
 infested. On February 5, 1911, the writer found the adults of this 
 insect extremely abundant in the pea field of some Chinese truckers 
 at Hollywood, Cal. Here nearly every plant had 7 or 8 adults feed- 
 ing on the underside of the foliage, and in many cases 5 and 6 were 
 present on each leaf. On August 18 of the same year in the same 
 locality plants of spiny wild lettuce (Lactuca scariola) were observed 
 that had 50 adults feeding on a single leaf. 
 
 The adults seem to feed on a large variety of plants and have been 
 found feeding on all of the plants given under " List of food plants." 
 It may be well to state at this point that the presence of adults on a 
 plant has not been considered sufficient evidence to class that plant 
 as a food plant, but whenever larvae of this insect were taken on a 
 plant, this was considered sufficient to rank the plant as a host. 
 
 In the spring when the adults leave hibernation they collect on 
 the wild food plants present and feed on them until their injury, 
 due to an increase in numbers and feeding, weakens the plants and 
 shortens the food supply; then they fly to fresh plants of the same 
 hosts or to cultivated crops and fruit trees nearby. Of all the food 
 plants observed, the spiny wild lettuce (Lactuca scariola} seems to 
 be the most favored. This plant has been found to be infested more 
 heavily than any of the other food plants concerned, not excepting 
 those of economic importance. 
 
 FLIGHT. 
 
 The present writer in his investigations of the greenhouse thrips > 
 never observed that insect to take flight naturally, or even when dis- 
 turbed. The adults of Heliothrips fasciatus, on the contrary, take 
 flight very readily, and if jarred or disturbed will usually fly or jump. 
 This species in taking flight raises the tip of the abdomen quickly, 
 and separates the wings. It then rises straight up into the air and 
 flies rapidly away in short undulating curves. Indeed, to the un- 
 trained eye it appears, in flight, exactly like a small speck of soot 
 being blown around by a slight breeze. This power of flight aids 
 greatly in the dispersion of this insect during the spring and summer. 
 
 Loc. cit.
 
 22 
 
 THE BEAN THRIPS. 
 
 This species possesses the power to leap actively and, considering 
 its size, to a considerable distance. It is no uncommon occurrence for 
 the specimens which are being examined upon a plant to leap off and 
 be lost. Like the greenhouse thrips, it will crawl over the leaves 
 rapidly when disturbed. At other times it will remain motionless 
 for a considerable period, lying closely to the surface of the leaf along 
 one of the veins. 
 
 NORMAL LENGTH OF LIFE. 
 
 The length of life of this insect as an adult has been determined 
 under the artificial conditions of confinement in vials containing 
 fresh leaves of the food plant. As often as these lost their freshness 
 other leaves were put in and the adults were changed with a camel 's- 
 hair brush. 
 
 Even under these conditions the length of life observed for some 
 individuals was surprisingly long, when we consider the minute size 
 of the insect. During these experiments it was observed that these 
 insects were very sensitive to humidity or a lack of it and all were 
 soon killed whenever the vials used in confining them became too dry. 
 Table II shows the results of these experiments in which some thrips 
 lived for 84 days. 
 
 TABLE II. Length of life of adult ~bcan thrips a<t Compton, Cal., 1911. 
 
 Bate adults emerged from pupa. 
 
 Number 
 emerged. 
 
 Specimens died. 
 
 Last 
 adult 
 died. 
 
 Maximum 
 length of 
 life. 
 
 Date. 
 
 Number. 
 
 
 
 
 
 
 Days. 
 
 April Id 
 
 3 
 
 /Mav 8 
 \May 11 
 
 1 
 1 
 
 }May 22 
 
 37 
 
 
 
 
 May 8 
 
 \ 2 4 
 
 
 
 April 2:$ 
 
 11 
 
 Mav 18 
 
 
 bulv 143 
 
 ' 
 
 84 
 
 
 
 May 26 
 
 1 
 
 
 
 
 
 June 5 
 
 1 
 
 J 
 
 
 June 5 
 
 '/June 17 
 ' \June 21 
 
 5 
 3 
 
 }Aug. 14 
 
 71 
 
 
 [July 22 
 
 
 
 
 
 July 25 
 
 2 
 
 
 
 July 19 
 
 14 Jjuly 26 
 4 jlAup. 8 
 
 2 
 
 Aug. 21 
 
 34 
 
 
 Aug. 12 
 
 2 
 
 
 
 
 I Aug. 17 
 
 1 
 
 
 
 Male and female. 
 
 LENGTH OF LIFE IN WINTER. 
 
 A number of adults were collected from host plants on November 
 18, 1910, and were placed in vials and furnished with fresh leaves at 
 intervals, and some lived in confinement in this manner until Febru- 
 ary 1, 1911, by which time all had died. On January 16, 1911, a num-
 
 HABITS OF THE LARVA. 23 
 
 her of adults were taken from the open on leaves of nasturtium and 
 were placed in vials. These died in April, giving a length of life 
 after being collected of 92 days. As adults have never been ol.-rv,,l 
 to emerge from pupae later than December 27, these adults must h;m- 
 been at least 21 days old when collected, so that they lived about 113 
 days. Probably hibernating individuals live as long as 5 months. 
 
 HABITS OF THE LARVA. 
 
 In observing the habits of the larva of this thrips, the writer was 
 constantly impressed with the great similarity that existed between 
 this species and the greenhouse thrips. This is so great that the 
 description of habits of the one would almost equally fit the other. 
 
 HATCHING. 
 
 Apparently the hatching process may occur at any time during 
 the day. Many have been observed hatching early in the morning 
 and one larva was observed emerging from the egg cavity at 4.25 
 p. m. Very slowly this larva pushed its way out of the egg cavity, 1 
 during which time the appendages were all held closely appressed 
 to the body and were invisible. As soon as the body was nearly out 
 the insect began a slow forward and backward movement and at 
 4.40 p. m. all but the tip of the abdomen was free, while the larva pro- 
 jected straight out from the leaf surface. While held in this position 
 it began slowly to unfold the limbs and antenna? and move them 
 around. The motion was very feeble at first, but gradually the larva 
 seemed to gain strength and at 4.48 p. m. it bent over and, grasping 
 the leaf surface, began to pull with its limbs in order to free itself. 
 This was accomplished at 4.53 p. m., making the total period required 
 in emerging from the egg 28 minutes. 
 
 The larvae of this insect after hatching move away a short distance, 
 then appear to rest for a few minutes until they become stronger. 
 Within a short time, however, they move on and soon commence 
 feeding. When first hatched the larva? are very minute and almost 
 colorless, but as they begin to feed and drain the green coloring 
 matter from the leaf the alimentary tract becomes plainly visible 
 from the contained food. In a few days the color of the body 
 becomes more or less yellowish and blotched with crimson. In com- 
 mon with other species of Heliothrips, the larvse of the present 
 species keep the tip of the abdomen elevated and carry around on it 
 a small globule of reddish liquid excrement. Gradually this globule 
 increases in size until it is too large to be carried any longer ami i' 
 falls to the leaf surface. Here in time it dries and forms a black 
 spot or scale. The occurrence of these spots on the leaf of a plant 
 
 iThis larva emerges from the egg by the same method that Is used by the conchuela 
 (Pentatoma ligata Say) as described by Morrlll (Bui. 8fi, Bur. Ent, U. S. Dept. , 
 38-39).
 
 24 THE BEAN THKIPS. 
 
 marked by feeding of some thrips furnishes good evidence that the 
 bean thrips has been feeding there at some time. The larvae feed in 
 much the same manner as the adult, the mouthparts being practically 
 the same. They gradually scrape out the contents of the leaf, leav- 
 ing silvery spots, which as they become abundant often unite and 
 gradually destroy the vitality of the leaf. Most of the eggs seem to 
 be laid on the underside of the leaves, although the writer has ob- 
 served eggs to hatch from the upper side also. As a consequence 
 the larva? begin feeding largely on the underside of the leaves. After 
 hatching they do not move far before commencing to feed, during 
 which time, under ordinary conditions, they move very little. When 
 plants are first infested the larva? seem to feed close to the leaf 
 veins, but as the} 7 become more abundant they scatter in groups over 
 the entire leaf surface. Like those of the greenhouse thrips the 
 larvoe of this species seem to cluster in colonies and unless disturbed, 
 or in need of fresh food, remain thus. The colonies are in many cases 
 found in between two veins of the leaves. When disturbed the lame 
 will violently twitch the end of the abdomen with its drop of liquid 
 and move away rapidly. Apparently this is used as a means of de- 
 fense, for the writer, in work with a parasite of this thrips, observed 
 at times that these larva? when touched from in front by the parasite 
 flung the abdomen around and moved rapidly away. When this oc- 
 curred the parasite generally retreated, but returned to the attack 
 and later usually succeeded in ovipositing in its host. 
 
 The larva? and adults of this thrips feed together in colonies, and 
 as the leaves become crowded or dry from excessive feeding the 
 larva? move in search of fresh food. Gradually the whole under- 
 side of the leaf attacked becomes infested by the larva? and then 
 the surface as well. In fact, the writer has seen leaves so heavily 
 infested by the larva? of this thrips as to give them a decidecUy 
 larva? move in search of fresh food food. Gradually the whole under 
 reddish color, due to the bodies of the insects. So far this larva 
 has not been observed feeding in the blossoms of any plant, 
 but in some cases it has been observed feeding on green tomatoes, 
 and when bean vines are badly infested the pods are also attacked. 
 Indeed, when excessively abundant, these insects will not only 
 cover both sides of the leaves^ but the stem of the plant as well. 
 The larvae, as a rule feed unprotected on the leaf, but at times may 
 be found feeding under the protection of red-spider webs. 
 
 Apparently these minute creatures are not affected by dust, as 
 the writer has found them feeding in large numbers on leaves of 
 spiny lettuce in an alley in the city of Los Angeles when the leaves 
 were so thickly covered with dust as completely to hide the surface. 
 It would seem that with the enormous clouds of dust that arise in 
 this section during the entire summer, completely coating the larva?, 
 they would speedily succumb.
 
 HABITS OF THE LARVA. 
 
 25 
 
 As an illustration of how abundant this insect may become the 
 following observations are given: On August 31, 1909 Mr Foster 
 of this bureau, found it severely infesting pear foliage at Martinez' 
 Cal., and noted as many as 200 larvae on one side of a leaf. On 
 July 28, 1910, the writer found some plants of spiny lettuce badly 
 infested by the larva? of this thrips, and 10 leaves gave a total infes- 
 tation of 733. (See Table III.) This gave an average of 73 3 to each 
 leaf. 
 
 TABLE III. Infestation of Lactuca scariola ly larva of the bran thri,,*. 
 
 No. of 
 leaf. 
 
 Number 
 of larvae 
 on under 
 side. 
 
 Number 
 of larvae 
 on upper 
 side. 
 
 Total 
 number of 
 larvae 
 on leaf. 
 
 No. of 
 leaf. 
 
 Number 
 of larvae 
 on under 
 side. 
 
 Number 
 of larva? 
 o^unper 
 
 Total 
 number 
 of larva) 
 on leaf. 
 
 1 
 2 
 3 
 4 
 5 
 
 70 
 34 
 43 
 30 
 59 
 
 7 
 39 
 2 
 2 
 
 47 
 
 77 
 73 
 45 
 32 
 106 
 
 7 
 8 
 9 
 10 
 
 44 
 61 
 70 
 23 
 
 47 
 30 
 
 1 
 32 
 
 91 
 91 
 
 71 
 55 
 
 6 
 
 46 
 
 46 
 
 92 
 
 
 480 
 
 253 
 
 733 
 
 On July 18, 1911, at Hollywood, Cal., leaves of spiny lettuce were 
 found that had several hundred larva? to a leaf. September 22, 1910, 
 Mr. Wildermuth observed a field of cotton at El Centre, Cal., show- 
 ing considerable injury by this insect, and counted as many as 200 
 larvae to a single leaf. 
 
 MOLTING. 
 
 The larva molts once, giving two larval instars, then molts to the 
 prepupal stage. On July 28, 1910, a number of larvae that had just 
 hatched were separated and on August 2 these all molted. On August 
 7 they again molted and changed to prepupae. This gave the first 
 instar a length of five days and the second a length of five days. The 
 process of molting in the larva is continued unprotected in the midst 
 of the feeding colony. After molting the skin is left adhering to the 
 leaf beside the feeding larva. 
 
 It was observed with the larva? of this species and of those of the 
 greenhouse thrips that when they were exposed to a low temperature 
 the entire development was checked and growth remained stationary 
 during the exposure. In long-continued exposures the insect* were 
 killed, but if within three weeks they were again removed to higher 
 temperatures the larvae resumed their growth and pupated in a 
 few days. 
 
 Under the artificial conditions of rearing in vials the mature 
 larvae seek concealment before pupation in curled-up leaves, in all 
 kinds of protected places, and if in vials closed with cotton plugs 
 they work their way in between the plug and side of the vial. In 
 the field, however, the larvae when full grown desert the plants and 
 hide in rubbish and cracks in the ground or beneath clods of earth. 
 51097 Bull. H812 4
 
 26 THE BEAN THEIPS. 
 
 The molting from larva to prepupa under laboratory conditions has 
 been observed many times. On April 10, 1911, a mature larva was 
 observed to begin the process at 4.05 in the afternoon. After remain- 
 ing motionless for some time it arched its body, and shortly after 
 the skin split down the head behind the antennae. The head grad- 
 ually forced its way out of the opening, then the body followed, the 
 old skin being slipped off behind. This molting was completed at 
 4.21 p. m. 
 
 HABITS OF THE PREPUPA AND PUPA. 
 
 The prepupae of this insect are found in company with the pupae 
 and full-grown larvae in small social colonies. These hold the 
 antenna? out in front of the body and move about to some extent. 
 The pupas, however, carry the antennae folded back on the head and 
 thorax and remain motionless unless disturbed or exposed to the 
 light, in which cases they will slowly crawl away. When com- 
 pelled to pupate in closed vials the prepupa3 and pupae occur in 
 large numbers closely packed together along the edge of the vial 
 and the cotton plug or buried in the cotton itself. In nature it has 
 quite different habits. While the greenhouse thrips under natural 
 conditions pupates on the leaf of the food plant in among the feeding 
 larva?, with the bean thrips this seldom takes place, and during the 
 two years this species has been under observation by the writer only 
 three pupae have been found on the plants infested by hundreds of 
 thousands of larvae. In one case a pupa was found under the web of 
 the red spider near the midrib of a leaf of spiny lettuce ; in another, 
 one was found under a web of red spider on a leaf of the wild tobacco 
 flower; and the third was found in a curled-up lettuce leaf. 
 
 December 17, 1910, a quantity of the dead leaves of wild helio- 
 trope Avere collected on the ground under infested plants. Prolonged 
 sifting revealed the presence of a single pupa. In 1911, the prepupae 
 and pupa? were found by Mr. John E. Graf and the writer to be 
 very abundant in infested bean fields under clods or lumps of dry 
 earth and in cracks or holes in the lumps. Upon exposure to the 
 light these at once began to move away in search of darkness. 
 
 Mr. Wildermuth also found the pupae of this insect underground. 
 He wrote in his notes on September 23 : 
 
 While searching by aid of a binocular for pupae, I found one pupa, one 
 prepupa, and two (mature) larvae just at the crown of the plant and beneath 
 the soil; one pupa about one-fourth inch below the surface of the soil in an 
 oval cavity about three times as long as the pupa itself; one prepupa between a 
 dead leaf and the soil. Never have I found a pupa above the surface of the 
 ground, on the leaves of the plant, or between the sheath leaves and the stem, 
 as frequently occurs in confinement. 
 
 The molting of the prepupa to the pupal stage is very similar to 
 that described for the change of the larva to the prepupa. It takes
 
 FOOD PLANTS. 27 
 
 place in whatever location the prepupa may be, and the transmit 
 and delicate empty skin is found behind the pupa. It was observed 
 during the fall that pupae exposed to a low temperature did not com- 
 plete their development to the adult stage. These, when later placed 
 in the greenhouse, changed to adults unless exposed to the unfavorable 
 conditions too long, when all were killed. 
 
 During the pupal stage several external changes take place. Vt 
 first the ocelli are not evident, but as the pupa develops these become 
 prominent in a triangle between the folded antennae. Then the reticu- 
 lations of the body begin to appear, and within two days of the 
 emergence of the adult the pupa begins to darken and the legs, 
 antennae, and wings begin to show blackish bands. The adult 
 emerges in a manner similar to the molting of the larva. Emerircncc 
 has been noted at all hours of the day, and there seems to be ^"par- 
 ticular time for its occurrence. 
 
 FOOD PLANTS. 
 
 This insect seems to be nearly as omnivorous as the onion thrips. 
 as the following list of food plants upon which it has been reared <>r 
 observed during the past two years by the writer would indicate. 
 These have been divided into economic and wild food plants, and 
 under each will be given notes on injury and appearance of injured 
 plants. 
 
 BEANS. 
 
 The injurious occurrence of this insect on the foliage of beans <ri ve- 
 to it its common name. It has been observed by the writer to feed on 
 bean foliage in the adult and larval stages from early in February, 
 in sheltered places, until the plants a-re killed by frost in the fall. 
 In the spring the wild plants are first up, and the attack is largely 
 concentrated on them, so that when the beans come up they are not 
 immediately attacked. However, in a few weeks the insect spreads 
 to the beans, thereafter increasing in numbers until in the late sum- 
 mer and fall much injury is done. When snap beans are infested 
 the adults first attack the leaves, and while feeding lay countless rirgs 
 in the tissue. The larvae on hatching begin to feed, and gradually 
 the green coloring matter is entirely removed from the underside >f 
 the leaf. This becomes white and covered with the black spots of 
 excrement. The infestation then spreads to the surface and to other 
 parts of the plant. As the feeding goes on the leaves lose all color, 
 become wdiite, or dry up and turn brown and drop off. As the infes- 
 tation increases, the stems and pods themselves are also attacked and 
 ruined. A badly infested field appears as if scorched by fire.- The 
 lima bean and pink bean suffer in the same way. The blackeye cow- 
 peas this past season were almost immune from the attack of this 
 insect, even in fields in which the pink beans and spiny lettuce were 
 very badly infested.
 
 28 THE BEAN THEIPS. 
 
 OTHER VEGETABLES. 
 
 During the spring and early summer this insect is not noticeable 
 on either the sugar or table beets. Late in the summer, however, as 
 the wild plants die down, these plants often become badly infested, 
 but as the beets have nearly completed their growth little real in- 
 jury results. The outside leaves seem to be first infested, showing 
 series of minute white spots more or less in chains, where the chloro- 
 phyll has been removed, but in badly infested leaves the underside 
 becomes white and dried and covered with small black spots, causing 
 the leaves to wilt. Mr. Parker wrote from Hamilton City, Cal., 
 under date of September 18, 1911, that the injury was apparent in 
 almost every field. 
 
 Cabbages and other crucifers are commonly infested by this thrips 
 and at times may be seriously injured. On March 27, 1911, cabbages 
 in the laboratory yard were slightly infested. Where they had fed 
 long the underside of the leaf was full of the silvery-white feeding 
 marks of this insect and the tiny black specks of excrement. Cauli- 
 flower suffers to the same extent as the less valuable cabbage. 
 
 This insect has also been found feeding quite extensively on let- 
 tuce, potato, and tomato. At Hollywood, Cal., in February, 1911, 
 it was very abundant on the foliage of pea vines, but the infestation 
 did not appear to increase, probably because the vines were quite old. 
 
 PEAR. 
 
 Mr. S. W. Foster found pear foliage badly injured on August 31, 
 1909, at Martinez, Cal. He wrote: 
 
 The foliage gave the appearance from a distance of having been scalded. 
 Close examination showed that the leaves were often injured in large areas on 
 either or both surfaces. The larvae, feeding only on these outer surfaces, soon 
 cause the blackened areas. 
 
 As the tree has made most of its growth for the season and the fruit crop 
 has been harvested, it is hardly probable that this species will prove of serious 
 consequence to the growers unless it should get so numerous as to appear in 
 numbers early in the season. 
 
 The following field observations on the work of the bean thrips 
 on alfalfa and cotton were made by Mr. Wildermuth in the Imperial 
 Valley, Cal.: 
 
 August 2, 1910. This thrips does nearly all if not all of its feeding on the 
 upper surface of the leaf. The excrement is arranged in definite rows, often 
 semicircular in form, around these eaten spots and makes a very characteristic 
 mark [see fig. 9]. The eaten spots later turn yellow and then the alfalfa 
 presents a sickly appearance. August 4 I visited several alfalfa fields and all 
 were very much injured by this thrips. Scarcely a leaf could be found that
 
 POOD PLANTS. 29 
 
 was green arid fresh as it should be TliP 
 
 FIG. 9. Alfalfa showing Injury by the bean thrips. (Original.) 
 
 of attack. September 30 the fields were still being b.-ully damaged. After a 
 field is newly irrigated just after cutting for a week or 10 days the dnuuivo is 
 not noticeable, but after three weeks nearly all leaves show the effects and tin- 
 alfalfa presents a very sickly appearance. A lack of sufficient water causes 
 the damage to be more noticeable, as under such a condition the growth of the 
 alfalfa is not so rapid and the thrips' damage is more conspicuous.
 
 30 THE BEAN THEIPS. 
 
 On September 18. 1911, he wrote: 
 
 This thrips is very abundant in alfalfa fields at this time of year, the larva? 
 being present on the older alfalfa and the adults present on the younger shoots 
 and leaves. Many leaves, after being badly scarred by the thrips, wilt and fall 
 off, so that the damage is soon very great. It seems rather strange that this 
 thrips should become so vary abundant in the fall of the year and Euthripa 
 tritici, the other important alfalfa thrips, should decrease in numbers and 
 that in the spring of the year just the opposite should be the case. 
 
 COTTON. 
 
 September 22, 1910, Mr. Wildermuth wrote : 
 
 This thrips was found damaging cotton about 11 miles southeast of El 
 Centre, Cal. The cotton was only damaged in one corner of the field, and it 
 happens that fresh alfalfa is being stacked close to this corner. 
 
 September 28 a field of cotton east of Imperial had a strip through the center 
 of the field damaged by this thrips. September 30 numerous fields on the east 
 side of the valley were being damaged by this pest. The leaves were dead and 
 rusty looking and the plants in bad condition. The damage was not as great as 
 if the work had begun earlier in the season, but was at that time very great. 
 
 October 11 several cotton fields at Holtville, on the east side of the valley, 
 were examined. A great many fields showed considerable injury. The leaves 
 were eaten and turned a sickly yellowish or brown, many often being curled. 
 A field on the Young ranch was as badly damaged as any seen, and this field 
 lay alongside an alfalfa field. Three other fields on the same ranch showed 
 very little damage. The former field was of a late planting. This thrips has 
 caused much more damage to cotton than was anticipated, and if it should 
 begin its work early in the season it might prove extremely destructive. Be- 
 cause of this, as well as other still better reasons, cotton should be planted as 
 early as possible in the spring. 
 
 In November. 1911, Mr. Wildermuth wrote: 
 
 Mr. Packard and cotton growers throughout the valley report but little injury 
 to cotton by this thrips this year. I found only two specimens of larvae myself, 
 and a few adults. It would seem as if the damage to cotton coines when cotton 
 follows alfalfa. This year, there being but little alfalfa laud put *o cotton 
 and more cotton following cotton, the damage was not so noticeable. 
 
 WILD PLANTS. 
 
 Of all food plants of this insect the wild spiny lettuce (Lactuca 
 scariola} seems to be preferred, at least in the vicinity of Los Angeles. 
 From early spring, when this plant comes up, until it dies down in 
 the fall, it is usually badly infested by thrips. Many cases have been 
 observed where other food plants, such as beans, etc., in the same field 
 were only slightly infested, while the spiny lettuce near by was so 
 badly attacked that many plants were dead. Furthermore, this weed 
 is one of the commonest in the country, occurring abundantly in un- 
 cultivated or even in badly cultivated fields. In addition it grows 
 up in dense clumps in all fence rows and roadsides, and the rights 
 of way of the different railroads are densely packed by this plant.
 
 SEASONAL HISTORY AT COMPTON, CAL. 31 
 
 When this weed first comes up in the early spring there is scarcely 
 any vegetation, so that it offers an agreeable host to the bean thrips, 
 especially as the foliage is very tender and juicy at that time. The 
 thrips attack the first young leaves, and the larvae, upon hatching 
 from eggs deposited at that time, join the feeding adults. As soon 
 as these become abundant, the leaves lose all or nearly all of the green 
 leaf-content and turn white, after which they dry up and hang dead 
 from the stalk. The infestation continues to spread to the younger 
 leaves until the entire plant is killed. 
 
 The sow thistle (Sonchus oleraceus) has the same general distri- 
 bution and is also a favorite food plant. 
 
 Wild heliotrope (Heliotropium curassavicum) is another favorite 
 food plant late in the year. This plant does not start in the spring 
 until quite late, and when it does appear above the ground generally 
 escapes destruction by cultivation. Thus it occurs commonly in the 
 beet and bean fields and in orchards, and in the fall is one of the 
 chief food plants. 
 
 The bean thrips has also been found feeding and reproducing in 
 numbers on Euryptera lucida and on one of the cucurbitacea?, prob- 
 ably an Echinocystis, in a canyon north of Los Angeles. In the same 
 locality it was later taken feeding and reproducing on Gnaphalinm 
 calif ornicum, Mirdbilis californica, Eunamis brevipcs, Chenopodimn 
 murale, Helianthus annuus, Atriplex sp., wild turnip, Erigeron cana- 
 densis, and wild pea (Lotus americanus} . It was also taken in the 
 valleys feeding and reproducing on the Chinese cigarette flower (Nic- 
 otiana glauca] , Bidens pilosa, Verbascum virgatum,, Polygonum avi- 
 culare, and Crepsis (?) sp. The adults were also taken in the fall 
 feeding on the foliage of a porch vine, Tacsonia mellissimus, and on 
 the cultivated nasturtium (Tropceolum major}. Mr. A. C. Morgan 
 found it on the underside of the leaves of the tulip poplar at Clarks- 
 ville. Tenn. 
 
 This thrips has also been recorded as feeding on Lotu* glalcr, 
 apple, peach, orange, wild vetch, burr clover, and radish. 
 
 After perusal of the above list of food plants it is easy to see how 
 this insect can obtain a foothold in a cultivated crop in the late 
 summer, especially as many of the wild plants die from maturity or 
 lack of moisture, thus forcing the insect to migrate. 
 
 SEASONAL HISTOBY AT COMPTON, CAL. 
 
 The life cycle of the bean thrips was observed at Compton for vary- 
 ing parts of the year, and because of the cooler and more even tem- 
 perature prevailing there is quite extended and more nearly equa 
 for the entire period of reproductive activity. 
 
 THE EGG. 
 
 The length of time required for the egg to hatch in the months of 
 March, April, and May was not exactly determined. However, fr
 
 32 
 
 THE BEAN THEIPS. 
 
 leaves of wild lettuce were collected on April 7 and they had a 
 number of eggs in them very recently laid. The last of these hatched 
 on April 24, making the length of incubation about 17 days, or possi- 
 bly as many as 21 days. The average mean temperature for these 
 21 days was 59.1 F. 
 
 In July several adults of this thrips were confined over night on 
 leaves of growing plants that were uninfested, and were removed 
 on the following morning. In this way a number of eggs were ob- 
 tained that hatched under absolutely normal conditions, ns the plants 
 were kept in an open-air insectary. 
 
 Table IV has been prepared to show the records of incubation for 
 these eggs. 
 
 TABLE IV. Length of egg stage of the bean thrips in July at Compton, CaL, 191 J. 
 
 
 Dates eggs hatched and number each day. 
 
 
 
 
 
 
 Date of 
 ovipo- 
 sition. 
 
 
 First egg 
 hatched. 
 
 Last egg 
 hatched. 
 
 Shortest 
 incuba- 
 tion. 
 
 Longest 
 incuba- 
 tion. 
 
 Total 
 eggs 
 hatched. 
 
 Julv 
 
 Julv 
 
 Julv 
 
 July' July 
 
 July 
 
 July 
 
 July 
 
 
 23. 
 
 24. 
 
 25. 
 
 26. 
 
 27. 
 
 28. 
 
 29. 
 
 30. 
 
 
 
 
 
 July 10 
 
 5 
 
 54 
 
 16 
 
 3 
 
 2 
 
 6 
 
 
 
 July 23 
 
 Days. 
 Julv 28 13 
 
 Days. 
 18 
 
 M 
 
 July 11 
 
 
 26 
 
 18 
 
 9 
 
 7 
 
 
 
 
 July 24 
 
 July 27 13 
 
 17 60 
 
 July 14 
 
 
 
 
 
 
 8 
 
 15 
 
 
 July 28 
 
 July 29 13 
 
 14 23 
 
 
 
 
 
 
 
 
 
 
 
 
 169 
 
 In this experiment 169 eggs hatched and the minimum length of 
 incubation was 13 days and the maximum 18 days, but nearly 50 
 per cent hatched in just 14 days. During this total period the aver- 
 age mean temperature was 69.6 F. 
 
 Again, on August 20 adults were confined over night on a living 
 plant of wild lettuce, and 4 larvse hatched on September 4, and 7 on 
 September 5, making the periods of incubation 15 and 16 days. 
 During this time the average mean temperature was 66.3 F. 
 
 During the months of October and November the incubation is 
 probably lengthened a few days and will take about 21 days, as the 
 average moan temperature for these months was, respectively, 58.67 
 and 55.3 F. 
 
 THE LARVA. 
 
 The length of time occupied by this insect in the larval stage dur- 
 ing the months of March, April, and May was observed during the 
 year 1911 by confining larvae that had just emerged in vials con- 
 stantly supplied with fresh food. Table V gives the results of these 
 observations. While in the first part of this period the length re- 
 quired was from 17 to 19 days, later it was shortened to 9 and 11 
 days. The average mean temperature for the first period, March 
 19 to April 7, was 61.5 F. and for May 14 to May 27 it was 61.1 F.
 
 SEASONAL HISTORY AT COMPTON, CAL. 
 
 33 
 
 TABLE V. Length of larval stage of the bean ///n'/w. Compton, Co?., March and 
 May, 1911. 
 
 Date larvae hatched. 
 
 Number 
 of larvae 
 hatched. 
 
 Larvae pupating. 
 
 Length stage. 
 
 Average 
 mean 
 temppra- 
 ture. 
 
 Date. 
 
 Number. 
 
 Minimum. 
 
 Maximum. 
 
 Mar. 19 
 
 8 
 
 7 
 15 
 14 
 
 (Apr. 5 
 {Apr. ti 
 Upr. V 
 May 24 
 /May 26 
 \Mav 27 
 May 27 
 
 
 . 
 
 17 
 
 10 
 
 1 " 
 
 Day,. 
 19 
 
 1 " 
 
 11 
 
 jr. 
 
 61.5 
 
 62.1 
 62.1 
 
 May 14 
 
 May 16 
 
 May 18 
 
 i Kest killed by heat. 
 
 During June and the first part of July this method of rearing 
 larvae to secure the length of instars was repeated, with the results 
 shown in Table VI. 
 
 TABLE VI. Length of larval stage of the bean thrii>* in June and the firxt part 
 of July, 1911, Compton, Cal. 
 
 Exp. 
 
 No 
 
 Eggs hatched. 
 
 Larvae pupated. 
 
 Total 
 pupated. 
 
 Duration of stage. A verage 
 mean 
 
 Date. 
 
 Number. 
 
 Date. 
 
 Number. 
 
 Minimum. 
 
 tempera- 
 Maximum, ture. 
 
 1 
 2 
 
 June 15 
 
 5 
 - 50 
 
 50 
 50 
 
 /June 28 
 \July 1 
 {July 10 
 July 11 
 July 12 
 (July 11 
 \July 12 
 July 13 
 
 1 
 
 j 
 
 4 
 3 
 
 2 
 
 11 
 
 11 
 3 
 
 Days. 
 13 
 
 11 
 
 11 
 12 
 
 Days. 'F. 
 
 :| - 
 
 June29 
 June 29 
 
 
 1 
 
 Here the minimum for the larval stage was 11 days and the maxi- 
 mum 14 days. 
 
 In July larvae were reared from eggs laid in normal growing 
 plants, situated in an outdoor insectary under normal conditions. 
 These experiments are all given in Table VII. 
 
 TABLE VII. Length of larval stage of the bean thrip* in July, 1911, at Compton, 
 
 Cal. 
 
 
 Eggs hatched. 
 
 Date and number of larvae 
 
 Total 
 larvae 
 
 Length of larval stage. 
 
 Average 
 mean 
 
 No. 
 
 Date. 
 
 Number. 
 
 pupating. 
 
 pupat- 
 ing. 
 
 Minimum. 
 
 Maximum. 
 
 ture. 
 
 
 
 
 
 Day,. 
 
 Days. 
 
 F. 
 
 1 
 
 [July 23 
 July 24 
 
 5 
 
 54 
 
 ) July 31. 85 larvae feeding; Aug. 
 I 2, all but 10 left plant to pu- 
 
 85 
 
 10 
 
 12 
 
 e.8 
 
 2 
 
 ljuly 25 
 July 24 
 July 25 
 July 26 
 
 16 
 26 
 18 
 9 
 
 | pate; Aug. 5, 10 prepupae. 
 (Aug. 2, all larvae left plant to 
 pupate in cracks. These lar- 
 \ vae were feeding from 7 to 9 
 ( days and then left the plant. 
 
 
 
 
 68.8 
 
 f 
 
 
 3 
 
 /July 28 
 July 29 
 
 8 
 15 
 
 Aug! 9, number of larvae pu- 
 pated. 
 
 
 11 
 
 
 } 66 ' 4 

 
 34 
 
 THE BEAN THKIPS. 
 
 In these experiments the larvae were observed to feed for a period 
 of 9 to 10 days and then to leave the plant to pupate, and 10 to 12 
 days were required between hatching from the egg and changing to 
 'prepupa?. 
 
 During the year 1910 a number of larvae that hatched on July 28 
 were observed to change to prepupjc on August 7, the total length 
 of the larval stage being 10 days, with an average mean temperature 
 of 72.1 F. 
 
 The length of this stage later in the summer and in early fall 
 for this locality unfortunately was not observed, but was probably 
 somewhat shorter for August and September and considerably 
 longer in October and November. 
 
 THE PREPUPA AND PUPA. 
 
 As the prepupa and pupa are two distinct stages, although closely 
 related, the length of each was separately determined. These two 
 stages during the spring of 1911 required from 3 to 6 days for the 
 prepupa and from 9 to 14 days for the pupa, or a total of from 14 
 to 19 days. The results are shown in Table VIII, with the average 
 mean temperature for each experiment. 
 
 TABLE VIII. Length of prepupal and pupal stages of the bean thrips at Comp- 
 ton, C'dl., during March to May, 1911. 
 
 Larvse changed to pre- 
 pupa\ 
 
 Prepupae 
 changed to 
 to pupae. 
 
 Adults 
 emerged. 
 
 Length of stage. 
 
 Average 
 
 Exp 
 
 
 
 
 
 
 Date. 
 
 Num- 
 ber. 
 
 Date. 
 
 Num- 
 ber. 
 
 Date. 
 
 Num- 
 ber. 
 
 Pre- 
 pupal. 
 
 Pupal. 
 
 Total. 
 
 ture. 
 
 
 
 
 
 
 
 
 Days. 
 
 Days. 
 
 Days. 
 
 P. 
 
 1 
 
 Mar. 31 
 
 5 
 
 Apr. 3 
 
 5 
 
 Apr. 17 
 
 5 
 
 3 
 
 14 
 
 17 
 
 59.2 
 
 2 
 
 \pr 10 
 
 1 
 
 \pr 15 
 
 
 \pr 24 
 
 
 5 
 
 9 
 
 14 
 
 59 5 
 
 
 Apr. 19 
 
 1 
 
 Apr. 25 
 
 j 
 
 May 4 
 
 1 
 
 6 
 
 9 
 
 15 
 
 57.9 
 
 4 
 
 Apr. 24 
 
 2 
 
 Apr. 29 
 
 1 
 
 May 10 
 
 1 
 
 5 
 
 11 
 
 16 
 
 56.9 
 
 
 Total 
 
 9 
 
 
 8 
 
 
 8 
 
 
 
 
 
 
 
 
 
 In the month of July these stages required from 1 to 4 days for the 
 prepupa, and from 4 to 7 days for the pupa, or a total of from 5 to 11 
 days. The number that required less than 7 days, however, was very 
 small. During this month the average mean temperature was G9 F. 
 
 Table IX shows the results of these experiments and the average 
 temperature for each.
 
 SEASONAL HISTORY AT COMPTON, CAL. 35 
 
 TABLE IX. Length of prepupal and pupal singes of the bean thrips at Comp- 
 ton, Cal., during July, J<)11. 
 
 Erp. 
 
 Changed to prepupa. 
 
 Changed to 
 pupa. 
 
 Adults 
 emerged. 
 
 Length of stage. 
 
 Average 
 
 No. 
 
 Date. 
 
 Num- 
 ber. 
 
 Date. 
 
 Num- 
 ber. 
 
 Date. 
 
 Num- 
 ber. 
 
 Pre- 
 pupal. 
 
 Pupal. 
 
 Total. 
 
 tempera- 
 ture. 
 
 
 
 
 
 
 
 
 Days. 
 
 Days. 
 
 Day,. 
 
 r. 
 
 
 July 1 
 
 7 
 
 July 5 
 
 7 
 
 /July 11 
 \July 12 
 
 2 
 5 
 
 f 4 
 
 6-7 
 
 10-11 
 
 71.7 
 
 
 July 10 
 
 3 
 
 July 13 
 
 3 
 
 July 18 
 
 3 ' 3 
 
 1 
 
 8 
 
 
 2 
 
 July 11 
 
 7 
 
 /July 14 
 \July 15 
 
 6 
 
 1 
 
 Wy IS 
 
 7 3 
 
 4 
 
 7 
 
 70.1 
 
 
 July 13 
 
 3 
 
 /July 14 
 \July 15 
 
 1 
 2 
 
 |july 19 
 
 1 ,- 2 
 
 4-5 
 
 5-7 
 
 
 
 3 
 
 4 
 
 /July 15 
 \July 10 
 July 19 
 
 1 
 
 2 
 2 
 
 July 17 
 July 18 
 July 23 
 July 24 
 
 1 
 1 
 2 
 
 July 24 
 July 24 
 July 29 
 July 29 
 
 1 
 1 
 
 2 
 
 2 
 
 2 
 2 
 3 
 3 
 
 6 
 6 
 5 
 
 9 
 8 
 9 
 
 8 
 
 71.8 
 63.5 
 
 July 20 
 
 During the month of August, 1010, at Los Angeles, CaL, larvae 
 changed to prepupaj August 2 and the adults emerged on August 9, 
 requiring 7 days for the prepupal and pupal stages. For this period 
 the average mean temperature at Compton, 10 miles out, was 72.4 F. 
 Another lot changed to prepupa on August 7 and the adults emerged 
 on August 15, giving a total of 8 days for the prepupal and pupal 
 stages. The average mean temperature at Compton for the period 
 was 71.4 F. 
 
 For the latter part of August and for September the length of these 
 stages is nearly that required in July. However, in October this 
 time is lengthened to some extent, Larvae that changed to prepupac 
 on November 3, 1910, required until November 1C before the adults 
 emerged, or a total of 13 days. The average mean temperature for 
 the period was 59.9 F. 
 
 Records made of the length of the prepupal and pupal stages for 
 November and December 1910, as given in Table X, show that at 
 that time of year the period required was greatly prolonged, the 
 prepupal stage requiring from 7 to 9 days and the pupal stage from 
 20 to 24 days, making a total period of from 27 to 33 days. During 
 this period the mean average temperature was 53.58 F. 
 
 TABIE X Length of prepupal and pupal ztagea of the VK-HH /ftri/w for \nrcmber, 
 1910, at Compton, Cal. 
 
 Exp. 
 No 
 
 1 
 2 
 
 3 
 
 Changed to prepupa. 
 
 Changed to pupa. 
 
 Adults emerged. 
 
 Length of stage. 
 
 Date. 
 
 Number. 
 
 Date. 
 
 Number. 
 
 Date. 
 
 Number. 
 
 Pre- 
 pupal. 
 
 Pupal. 
 
 Total. 
 
 *~* 
 
 27-29 
 
 30-33 
 
 Nov 14 
 
 1 
 2 
 
 7 
 
 Nov. 21 
 Nov. 23 
 (Nov. 25 
 JNOV. 26 
 t or 27. 
 
 1 
 2 
 
 4 
 2 
 
 Dec. 12 
 (Dec. 13 
 \Dec. 15 
 Dec. 15 
 Dec. 17 
 
 1 
 1 
 
 1 
 3 
 
 *, 
 
 \ 7 
 | 8-9 
 
 ** 
 
 20-22 
 
 22-24 
 
 Nov. 16 
 
 Nov.17 
 Total 
 
 10 
 
 9 
 
 7
 
 36 THE BEAN THKIPS. 
 
 TOTAL LIFE CYCLE. 
 
 For localities with climatic conditions similar to those of Compton, 
 the life cycle of this thrips will occupy during the early spring about 
 51 to 56 days, taking 20 days for the egg incubation, 17 to 19 days 
 for the larval development, and 14 to 17 days for the prepupal and 
 pupal stages. 
 
 During the months of June to October the life cycle of this thrips 
 will occupy from 28 to 43 days, taking 13 to 18 days for the egg 
 stage, 10 to 14 days for the larval stage, and 5 to 11 days for the 
 prepupal and pupal stages. 
 
 During the rest of the breeding activity the life cycle must be even 
 longer than in the spring, as in November, 1910, the prepupal and 
 pupal stages alone occupied from 28 to 33 days, so that for the de- 
 velopment of this insect during October, November, and the first of 
 December at least G8 to 73 days must be required. 
 
 EMERGENCE FROM HIBERNATION. 
 
 In 1912 the adults began to emerge from hibernation at Holly- 
 wood, Cal., in January, and began oviposition at once. When this 
 locality was visited on February 7, the adults were found to be feed- 
 ing on the foliage of peas and beans in some numbers. They were 
 also seen in copulation in many cases. A careful examination dis- 
 closed 4 young larva? feeding on bean foliage, so that the adult must 
 have laid the eggs at least by January 10. This fielcl was situated 
 on the foothills of w T hat is termed a frostless belt, and it may be that 
 tins insect in mild winters might breed there during the entire 
 period. 
 
 On February 17 adults were found feeding on pea foliage in Mis- 
 sion Valley, San Diego County, but no young w T ere seen. February 
 23 the species was found as an adult feeding on pea vines in the truck 
 farms around Los Angeles, and on March 13 adults w r ere found feed- 
 ing in small numbers at Compton, Cal. From then on the adults were 
 common feeding on different plants, but not until April 17 were the 
 larva 1 found feeding in the open at Compton, although they were 
 being reared in the open insectary at that place from material col- 
 lected at Hollywood. 
 
 It would probably be better to say that this insect begins active 
 reproduction at a varying time, those in the most protected places 
 starting as early as January 10, and the others over the next 60 days. 
 However, during the early spring the multiplication and spread 
 seem to be very slow. 
 
 ENTRANCE INTO HIBERNATION. 
 
 As the month of October appears, the adults become sluggish, do 
 less feeding and lay fewer eggs, and apparently many enter hiberna-
 
 SEASONAL HISTORY IN THE IMPERIAL VALLEY. 37 
 
 tion. The larvae become much less numerous and require an extended 
 period to complete their growth. In 1910 the last larvae in numbers 
 were observed in the field on November 20, while one was observed on 
 December 1, and three on December 13, and during the first part of 
 December these had all changed to pupae or died. The last adult 
 appeared on December 27. In 1911 the larvae were not very abundant 
 after the first week in October, and the last ones were observed in 
 Los Angeles County on November 21. 
 
 NUMBER OF GENERATIONS. 
 
 In the section of the State in which this insect was under observa- 
 tion, the first spring generation may commence as early as January 
 10 and probably egg-laying by overwintering adults continues for a 
 considerable time. As the period of oviposition is quite extended the 
 different broods tend to overlap ; still in midsummer there are certain 
 periods when the majority of thrips present may be adults or larvae. 
 Up to April 1 there is probably one small full generation occupying 
 about 56 days. During April and May a second generation will 
 develop; then during the four months of June, July, August, and 
 September there is one full generation for each month. For the rest 
 of the period of the breeding activity we have probably a partial 
 brood that extends over 68 to 73 days. 
 
 Thus during the year this insect has a small generation in both the 
 early spring and late fall and five full generations during the rest of 
 the time, or seven generations a year. 
 
 SEASONAL HISTORY IN THE IMPERIAL VALLEY. 
 
 The observations on the life cycle of this insect for Imperial Valley 
 were conducted by Mr. V. L. Wildermuth at El Centre, Cal., in 1910. 
 
 EGG PERIOD. 
 
 Mr. Wildermuth confined adults in vials with fresh sprigs of 
 alfalfa and kept the foliage fresh by wrapping the stems in moist 
 cotton until the larvae hatched from the eggs. While many eggs were 
 secured by this method, large numbers died before hatching, as the 
 foliage became too dry. but, as shown in Table XI, the egg stage 
 varied from four days in a single case to five days in a lot of 20 eggs 
 laid the last day of August. The length of the egg stage at that 
 locality was only one-third as great as that observed by the writer in 
 Los Angeles County, but this is clue in a large measure to the high 
 temperature of the Imperial Valley. 
 
 243602
 
 38 
 
 THE BEAN THRIPS. 
 
 TABLE XI. Length of incubation of the eggs of the lean thrips, El Centra, 
 
 Co?., 1910. 
 
 Dateofoviposition. 
 
 Number 
 laid. 
 
 Eggs hatched. 
 
 Length 
 of stage. 
 
 Average 
 mean 
 tempera- 
 ture. 
 
 Date. 
 
 Number. 
 
 
 2 
 
 ( 2 ) 
 .( 2 ) 
 
 Aug. 1 
 
 Aug. is 
 
 Sept. 6 
 
 2 
 
 1 
 20 
 
 D^ 
 
 5 
 
 "&.! 
 
 88.7 
 
 Aug. 11 
 
 
 Records missing. 
 
 Many. 
 
 3 At Brawley. 
 
 LARVAL, PERIOD. 
 
 The active feeding larva molts once before its final molt to the 
 prepupal stage. This occurs in from one and one-half to two days 
 after it hatches from the egg. The larva becomes full grown and 
 changes to the prepupa in from four and one-half to five days. As 
 might be expected from the great difference in the incubation period 
 of the egg, the larval period in the Imperial Valley, as observed by 
 Mr. Wildermuth, is much shorter than at Compton. These data 
 are given in Table XII. 
 
 TABLE XII. Length of larval stage of the bean thrips at El Centro, Cat., 
 during 1910. 
 
 Eggs hatched. 
 
 Molted. 
 
 Changed to 
 prepupa. 
 
 Length. 
 
 Average 
 mean 
 
 Date. 
 
 Number. 
 
 Date. 
 
 Number. 
 
 Date. 
 
 Number. 
 
 
 ature. 
 
 
 
 
 
 
 
 Days. 
 
 F. 
 
 Aug. 15 
 Aug. 18 
 Aug. 26 
 
 
 Aug. 16 
 Aug. 19 
 Aug. 28 
 
 
 Aug. 19 
 Aug. 22 
 Aug. 31 
 
 
 1 
 
 85.8 
 
 (1) 9i.o 
 
 Sept.l 
 Sept. 22 
 
 
 Sept. 3 
 Sept. 24 
 
 
 Sept. 5 
 Sept. 27 
 
 
 4 
 5 
 
 89.7 
 81.8 
 
 Total 
 
 7 
 
 
 5 
 
 
 5 
 
 
 
 
 
 1 Records missing. 
 
 PREPUPAL AND PUPAL PERIODS. 
 
 Unfortunately Mr. Wildermuth's records give a very small amount 
 of data on the length of the prepupal and pupal periods., but in the 
 six examples observed (see Table XIII) the stages varied from 2 
 to 3 days. While the writer was studying the greenhouse thrips 
 the prepupal stage was often observed to last only a few hours, and 
 this same condition probably occurs with the present species in the 
 high temperature of the Imperial Valley.
 
 HIBERNATION. 39 
 
 TABLE XIII. Length of prepupal and pupal stages, El Centra, CaL, 1910. 
 
 Exp. 
 No. 
 
 Date changed to prepupa. 
 
 Date 
 adult 
 emerged. 
 
 Length 
 of 
 period. 
 
 Average 
 mean 
 
 t'-:ri; . r- 
 ature. 
 
 1 
 
 Aug 19 
 
 
 Days. 
 2*-3 
 
 'F. 
 
 2 
 
 Aug. 22 
 
 AUK 24 
 
 2J-3 
 
 B 
 
 3 
 
 Sept. 6 
 
 Sept 8 
 
 2-24 
 
 '849 
 
 4 
 
 Sept. 4 
 
 <!',! S 
 
 3 
 
 *85 1 
 
 5 
 
 Sept 7 
 
 Sept 9 
 
 2 
 
 * 87 
 
 6 
 
 Sept. 27 
 
 Sept 29 
 
 2J 
 
 (') 
 
 
 
 
 
 
 1 Records missing. 
 
 ' Temperature at Brawley, U. S. Weather Bureau. 
 
 In the Imperial Valley the egg stage is from 4i to 5 days, the 
 larval stage from 4 to 5 days, and the prepupal and pupal stages 
 from 2 to 3 days, making the total life cycle only 10 to 12 days 
 during the extreme summer temperature. 
 
 The eggs were deposited within 2 days from the time the adult 
 females emerged, so that a new generation might occur every 14 
 days in midsummer. If the insect -emerges from hibernation in the 
 Imperial Valley at the same time as in Compton, there will un- 
 doubtedly be 1 generation in the early spring occupying 30 to 40 
 days, and then 2 generations a month for 5 or 6 months and 1 
 longer generation in the fall, or 12 to 14 generations a year. Indeed, 
 with such rapid multiplication it is not strange that crops in the 
 late fall become seriously infested. 
 
 SEASONAL HISTORY AT TEMPE, ARIZ. 
 
 Mr. Wildermuth during October and November, 1911, made some 
 observations on the life cycle of this thrips at Tempe. These gave 
 a life cycle of very nearly the same duration as in the Imperial Valley 
 in the warm weather, but in November the cycle was lengthened 
 considerably. He found that specimens collected as larvae on October 
 30 did not emerge as adults until December 1. This shows the same 
 effect of cooler weather on this insect that the writer observed at 
 Compton, Cal. 
 
 Taking the results of Mr. Wildermuth's and the writer's observa- 
 tions on the bean thrips, there is a minimum life cycle of 10 days 
 where the "average mean temperature is about 88.75 F., and a maxi- 
 mum of about 73 days with an average mean temperature of about 
 53.58 F. 
 
 HIBERNATION. 
 
 This insect hibernates as an adult only, through most of its dis- 
 tribution at least. It may be that in the more southern portions of 
 its range it breeds continuously throughout the year, but our obser- 
 vations in these localities mentioned have failed to show it
 
 40 THE BEAN THRIPS. 
 
 In the section around Compton, CaL, the adults were found to 
 hibernate in small numbers on the underside of leaves of nasturtium, 
 sugar beets, wild heliotrope, and other plants. They were also found 
 hiberating in some numbers in dead leaves and rubbish. When dis- 
 turbed they were sluggish and made little effort to escape. 
 
 Mr. P. R. Jones (in litt.) says that around Lindsay, CaL, the adults 
 hibernate in numbers in the navel end of the Washington navel 
 orange. He also stated that in midwinter he had taken this thrips 
 along creek beds hibernating on the underside of leaves of wild rasp- 
 berry and blackberry which were still on the plants. 
 
 NOTES ON OCCURRENCE. 
 
 Apparently the different methods of cultivation bear strongly on the 
 abundance of these insects and consequent injury they may cause to a. 
 crop. In Los Angeles County, where clean cultivation is not strictly 
 followed out, it begins to breed in the spring on the wild food plants 
 and increases more and more until in August it has reached enormous 
 numbers. Before this the native plants are, many of them, either 
 matured or destroyed by the thrips, and as a result it spreads more 
 and more to the cultivated crops and trees that serve as hosts. Dur- 
 ing some years this occurs late in the season and very little real 
 damage results, but if this insect should begin the year in fairly large 
 numbers and under favorable conditions, great damage may result. 
 
 In Ventura County, in October, 1910, the author made a careful 
 examination of the entire bean-growing section and found that the 
 bean thrips occurred in extremely small numbers on the little vege- 
 tation remaining. At the same time it was extremely abundant 
 around Compton. This condition seemed to be a direct result of the 
 practice of the growers in Ventura of thoroughly plowing and culti- 
 vating the fields within a short time after the beans are harvested 
 and keeping them in perfect condition until the next crop is planted. 
 This advantage is increased because there is very little waste space 
 where weeds can grow up. Our investigations during the past two 
 years have shown that this insect is not abundant on cultivated crops 
 in the spring or early summer, but that after this period it increases 
 more and more, and in certain years injures them so severely as to 
 cause much loss. 
 
 NATURAL CONTROL. 
 
 RAINS. 
 
 One of the largest factors in the destruction of thrips in some 
 localities is the prevalence of hard, dashing rains. The author, 
 while working in Florida with the greenhouse thrips, once observed
 
 NATURAL CONTROL. 41 
 
 that crotons, which in the greenhouse were infested with thousands 
 of thrips and which in June were placed outside and subjected to 
 the Florida summer rains, when examined in September were so free 
 from this insect that it was almost impossible to find specimens, 
 
 California, with its long dry season," does not obtain the same* 
 benefit, but even there the rains may reduce attacks of the bean thrips 
 to some extent. On February 7, 1911, the writer observed a pea 
 field that had from 5 to 8' adults on every plant. After this date 
 there was a severe rain of several days' duration, and when the 
 field was again examined, on April 1, it was almost impossible to 
 find the thrips. Mr. Graf, writing from Puente, Cal., on October 6, 
 1911, noted that the larvae were much scarcer than a week earlier, 
 probably owing to a rainfall of one-half inch. Mr. Wildermuth, 
 at Tempe, Ariz., wrote on October 5, 1911 : 
 
 A search in the patch of alfalfa back of the office, where thrips had been 
 very numerous for several weeks, failed to 'reveal very many thrips to-day. 
 The heavy raiu of yesterday and last night was probably responsible for 
 washing them off. 
 
 In California, then, late rains in the spring may greatly diminish 
 the numbers of this insect, or early rains in the fall destroy many 
 that otherwise would enter hi- 
 bernation. 
 
 NATURAL ENEMIES. 
 
 FIG. 10. The bean thrips : Prepupir parasit- 
 
 A great deal of attention has 
 been given to the subject of 
 natural enemies and some information obtained on this important 
 feature of insect control. 
 
 In the fall of 1910 the larva of this thrips was discovered to be 
 parasitized (see fig. 10) by a minute hymenopteron. This was de- 
 scribed by Mr. J. C. Crawford as Thripoctenus ru$selli (see fig. 11). 
 During 1911 this parasite was observed to work extensively in Los 
 Angeles County on the bean thrips and seemed to destroy large 
 numbers. Some collections of thrips larvae gave as high as 70 per 
 cent killed by the parasite. For a full account of this parasite the 
 reader is referred to Technical Series 23, Part II, Bureau of Ento- 
 mology, United States Department of Agriculture. 
 
 During 1911 the larva of a green lacewing fly (Chrysopa cal 
 fornica Coq.) was commonly observed feeding on the larva of this 
 thrips. As this insect was observed so engaged in several localities 
 in Los Angeles County, and in noticeable numbers, it probably k 
 a large number of thrips. 
 
 The larva of a syrphid fly (Sphayrophoria, sulphuripes Thou m) 
 wa's also observed on numerous occasions feeding on the larva of
 
 42 
 
 THE BEAN THRIPS. 
 
 the bean thrips, and in confinement larvae were observed to kill and 
 eat large numbers of the host. 
 
 The young of Triphleps insidiosus Say were noticed on many 
 occasions feeding on the young of this thrips and undoubtedly aid 
 *in reducing its numbers. 
 
 The larva? and adults of Hippodamia convergent Guer were fre- 
 quently collected on plants infested with thrips, where they were 
 busily engaged in feasting on the tender larva? of the bean thrips. 
 
 On several occasions larvas of a predaceous thrips, probably /Eolo- 
 thrips fasciatus L., when collected were feeding on the Iarva3 of the 
 bean thrips. 
 
 parasite, Thripoctenus runm-lli: Adult. 
 (Author's illustration.) 
 
 Greatly enlarged. 
 
 Mr. 1*. R. Jones informed the writer that at Lindsay, Cal., in 
 1910, he found a " nematode parasite working in the full-grown 
 larva* of the bean thrips." 
 
 A curious circumstance in connection with the observations made 
 on the natural enemies of the bean thrips was the fact that in all of 
 the predaceous forms noted the alimentary tract became bright red, 
 undoubtedly due to the crimson or reddish pigmentation of the host. 
 
 ARTIFICIAL CONTROL. 
 CULTURAL METHODS. 
 
 Iii the case of crops planted over large areas and difficult or im- 
 possible to spray, such as beans, alfalfa, or cotton, cultural methods 
 offer the most hope as a remedy for the bean thrips. Where this 
 insect threatens injury it is recommended that these methods be used 
 so far as possible. It is very important that the crops be given
 
 ARTIFICIAL CONTROL. 43 
 
 careful, clean cultivation, so that all weeds may be kept down in 
 the fields at all times, including the spring and fall. These same 
 weeds, especially the different species of wild lettuce, should be care- 
 fully destroyed along the edges of all fields and fence corners and 
 along the roads and railroad tracks. Cotton and beans should not 
 follow in old alfalfa fields if the latter were badly infested with the 
 bean thrips, and fields of these crops should be removed as far as 
 possible from the alfalfa fields. They should also be planted as 
 early as is consistent with good farming and encouraged by fre- 
 quent cultivations and fertilizers where necessary to produce an early 
 crop so as to escape the ravages of the bean thrips in the late summer. 
 
 As this insect feeds on such a variety of plants it is hardly pos- 
 sible that rotation of crops would aid materially in its control unless 
 some crop could be found that is quite immune. 
 
 Where it is injuring alfalfa Mr. Wildermuth recommends disking 
 and thorough renovation of the fields and good irrigation in order 
 to give the plants as much chance as possible to make a quick growth. 
 
 SPRAYING. 
 
 The control of this thrips by spraying is impracticable for a crop 
 such as alfalfa or cotton, and because of the low trailing vines of 
 the bean will probably be successful with this plant only when the 
 vines can be easily reached from the underside. In case injury to 
 fruit trees is threatened it can be controlled by using the spray so 
 successful against the pear thrips. This is a solution of 2| per cent 
 nicotine, diluted at the rate of 1 part to 60 parts of water in a 6 
 per cent distillate-oil emulsion. 1 
 
 The distillate-oil stock emulsion, according to the formula of 
 Foster and Jones, is made as follows : 
 
 Hot water -gallons.. 12 
 
 Fish-oil or whale-oil soap 
 
 Distillate-oil (raw) 30 to 34 Baum6 
 
 Have the water boiling hot when put into the spray tank and add the soap 
 immediately while the agitator is running at a good speed. When the soap Is 
 all thoroughly dissolved pour in the oil slowly, keeping the mixture well agi- 
 tated while the oil is going into the tank. When all of the oil is in and well 
 mixed, pump out through the nozzles at good pressure (not less 
 pounds) into storage tanks. 
 
 No one should attempt to make this stock emulsion without a power spra 
 machine, as thorough agitation and high pressure are important requisil 
 Also care should be used in having measurements reasonably exact, the water 
 boiling 'hot and the soap thoroughly dissolved before any oil is put In. 1 
 stock solution contains approximately 55 per cent oil, and to make a 3 per c< 
 emulsion use 5* gallons of this stock in each 100-gaIlon tank. 
 
 i For a' full account of this spray as used against the pear thrips. see Circular 131, 
 Bureau of Entomology, U. S. Dept. of Agriculture, pp. 8-0.
 
 44 THE BEAN THEIPS. 
 
 A simpler formula and one that possibly will act quite as well on 
 this insect, where it is exposed on the foliage, and one that will offer 
 no chance for the burning of the foliage, has given good results in 
 the destruction of Heliothrips rubrodnctus Giard in Florida. Mr. 
 Edward Simmonds, of the Bureau of Plant Industry, advised the 
 writer that a solution composed of 1 gallon of blackleaf tobacco ex- 
 tract, 1 pound of whale-oil soap, and 50 gallons of water gave excel- 
 lent results in treating trees infested by this insect. This formula 
 seems a little strong to the writer and he would recommend using the 
 blackleaf at the rate of 1 part to 60 parts of water. In the place of 
 this, a 40 per cent solution of nicotine can be substituted at the rate 
 of 1 part to from 1.000 to 2,000 parts of water-. 
 
 DISTRIBUTING THE PARASITE. 
 
 Possibly the parasite of this insect can be artificially distributed 
 with good results to sections infested by this thrips where the para- 
 site does not occur. For directions and methods of shipping this 
 parasite, the reader is referred to Technical Series 23, Part II, Bureau 
 of Entomology. U. S. Department of Agriculture, page 51. 
 
 BIBLIOGRAPHY. 
 
 :1. I'ERGANDE, THEODOHE. Insect Life, vol. 7, pp. 391-392, 1895. 
 Original description of the species. 
 
 '1. UZEL, ,T. Mon. der Orel. Thysan., p. 459, 1S95. 
 
 Copy of the original description of Pergande. 
 
 :',. HJNDS, W. E. Proc. IT. S. X^it. Mus., vol. 26, pp. 174-175. 3902. 
 Redescription of single female. 
 
 4. DANIEL, S. M. Ent. News, vol. 15, p. 294, 3904. 
 
 This author seems to have taken Pergande's records of locality and host 
 of this insect. 
 
 5. DANIEL, S. M. Ent. News, vol. 15, p. 297, 1904. 
 
 Described the male as a new species under the name Caliothrips woodicorthi. 
 <;. Mon/rox, DUDLEY. Tech Ser. 12, Bur. Ent., U. S. Dept. Agr., pp. 39, 43, 
 51, 52. PL II, figs. 12-14, 1907. 
 
 Records capture on orange, pea vines, and wild vetch and places Caliothrips 
 ivoodworthi as a synonym of H. Jasciatus. 
 
 7. CRAWFORD, D. L. Pomona Journ. Ent., vol. 1, pp. 120-121, 1909. 
 
 Records this species from pine foliage, Lotus {/laber, and blossom end of 
 ripe apple in southern California. 
 
 8. BREMNER, O. E. Destructive insects and their control. <Cal. State Corniu. 
 
 Hort, 1910. 
 
 This thrips, under the name Euthrips fasciatus, was recorded as injuring 
 peas and beans and occurring on alfalfa and peach and pear trees. 
 
 n. COIT, .1. ELIOT, and PACKARD, W. E. Cal. Agr. Exp. Sta., Bui. 210, pp. 168. 
 184, 1911. 
 
 This thrips, under the name Heliothrips fascietns (sic), recorded as injuring 
 alfalfa and cotton in the Imperial Valley, Cal. 
 
 10. MOULTON, DUDLEY. Tech. Set. 21, Bur. Eiit., U. S. Dept Agr., pp. 9, 14, 
 23-24. 
 
 Notes on synonymy and food plants.
 
 BIBLIOGRAPHY. 45 
 
 11. KARNY, H. Entomologische Rundsckuit, Jahrgang 28. p. 180, 1911. 
 
 Revision of the genus Heliothrips, with table of species Including fcuciatm. 
 
 12. RUSSELL, H. M. Proc. Ent. Soc. Wash., vol. 12, pp. 235-238, 1911. 
 
 A brief summary account of a parasite reared from Heliothrips fasciatus. 
 33. RUSSELL, H. M. Tech. Ser. 23, Pt. II, Bur. Ent., I*. S. Dept. Agr.. pp. ur. r,-j. 
 3912. 
 
 A very full account of the life history and habits of the parasite reared from 
 
 this thrips. 
 
 14. MOBRILL, A. W. Monthly Bui. State Hort. Comm. Cal.. vol. 1, no. 5. p. H52, 
 April, 1912 
 
 Heliothrips fasciatus Perg. is noted as one of the species affecting the 
 orange.
 
 INDEX. 
 
 .Eolothripsfasdatus, probable enemy of bean thrips 42 
 
 Alfalfa, food plant of bean thrips 16, 17, 28-30 
 
 Apple, food plant of bean thrips 16 31 
 
 crab, bean thrips taken thereon 17 
 
 Atnplex sp., food plant of bean thrips 31 
 
 Beans, food plant of bean thrips 16, 27 
 
 Beets, sugar, food plant of bean thrips 17, 28 
 
 table, food plant of bean thrips 28 
 
 Bidens pilosa, food plant of bean thrips 31 
 
 Cabbage, food plant of bean thrips 28 
 
 Caliothrips woodwort.hi, bibliographic references 44 
 
 synonym of Helioihrips fasdatus . 16 
 
 Cauliflower, food plant of bean thrips 28 
 
 Chenopodium murale, food plant of bean thrips 31 
 
 Chrysomphalus aurantii, association with bean thrips on orange leaf 16 
 
 Chrysopa calij "arnica, enemy of bean thrips 41 
 
 Cigarette flower, Chinese. (See Nicotiana gJauca.) 
 
 Clover, burr, food plant of bean thrips 31 
 
 Cotton, food plant of bean thrips 16, 17, 28-30 
 
 Crepsis (?) sp., food plant of bean thrips 31 
 
 Cultural methods in control of bean thrips 42-43 
 
 Distillate-oil emulsion against bean thrips 43 
 
 Echinocystis, probable food plant of bean thrips 31 
 
 Erigeron canadensis, food plant of bean thrips 31 
 
 Eunanus brevipes, food plant of bean thrips 31 
 
 Euryptera lucida, food plant of bean thrips 31 
 
 Euthripsfasciatm, bibliographic reference 44 
 
 =HeHothripsfasciatus 16 
 
 pyri. (See Thrips, pear.) 
 Fish-oil soap. (See Soap, whale-oil.) 
 
 Gnaphalium calif ornicum, food plant of bean thrips 31 
 
 Helianthus annuus, food plant of bean thrips 31 
 
 Helioihrips fasciatus. (See Thrips, bean.) 
 
 hsemorrhoidalis, larval habits 
 
 rubrocinctus, control by spraying 44 
 
 larval habits 9 
 
 Heliotrope, wild. (See Heliotropium curassavicum.) 
 
 Heliotropium curassavicum, food plant of bean thrips 
 
 Hippodamia convergens, enemy of bean thrips 
 
 Lacewing fly, green. (See Chrysopa calif ornica.) 
 Lactuca scariola. (See Lettuce, spiny wild.) 
 
 Lettuce, food plant of bean thrips 
 
 spiny wild, food plant of bean thrips 
 
 47
 
 48 THE BEAN THHIPR. 
 
 Page. 
 
 Lotus americanus, food plant of bean thrips 31 
 
 glaber, food plant of bean thrips 16, 31 
 
 Mirabilis calif ornica, food plant of bean thrips 31 
 
 Nasturtium. (See Tropasolum major.) 
 
 Nematode parasite, enemy of bean thrips 42 
 
 Nicotiana glauca, food plant of bean thrips 31 
 
 Nicotine solutions, against bean thrips 16 
 
 sulphate against bean thrips 16 
 
 Oil. (See Distillate oil and Soap, Whale-oil.) 
 
 Orange, food plant of bean thrips 31 
 
 Chrysomphalus aurantii 16 
 
 medium in dispersion of bean thrips 15 
 
 Parasite of bean thrips, artificial distribution 44 
 
 Peach, food plant of bean thrips 16, 31 
 
 Pea, food plant of bean thrips 14. 16, 28 
 
 wild. (See Lotus americanus.) 
 
 Pear, food plant of bean thrips 16. 17, 28 
 
 Pine, food plant of bean thrips 16 
 
 Polygonum aviculare, food plant of bean thrips 31 
 
 Poplar, tulip, bean thrips found thereon 31 
 
 Potato, food plant of bean thrips 28 
 
 Radish, food plant of bean thrips 31 
 
 Rains in control of bean thrips 40-41 
 
 Soap, whale-oil, and blackleaf tobacco extract against Heliothrips rubrocinctus 
 
 and bean thrips 44 
 
 Sonchus oleraceus, food plant of bean thrips 31 
 
 S phscrophoria sulphuripes, enemy of bean thrips 41-42 
 
 Tacsonia mellissimus, food plant of bean thrips 31 
 
 Thistle, sow. (See Sonchus oleraceus.) 
 
 Thripoctenus russelli, artificial distribution 44 
 
 parasite of bean thrips 16, 41, 42 
 
 Thrips, bean, adult female, description 9 
 
 habits 17-23 
 
 male, description 10 
 
 adults, recently described, description 10 
 
 bibliography 44-45 
 
 control, artificial 42-44 
 
 natural 40-42 
 
 description 8-9 
 
 distribution 14-16 
 
 egg, description 10 
 
 hatching 23-25 
 
 stage, length at Compton, Cal 31-32 
 
 in Imperial Valley 37-38 
 
 enemies, natural 41-42 
 
 feeding habits 20-21 
 
 flight 21 
 
 food plants 27-31 
 
 generations, number, at Compton, Cal 37 
 
 habits of adult 17-23 
 
 larva 23-26 
 
 prepupa and pupa 26-27 
 
 hatching of eggs 23-25
 
 INDEX. 49 
 
 Thrips, bean, hibernation 
 
 emergence therefrom, at Compton, Cal 36 
 
 entrance, at Compton, Cal 36-37 
 
 in navel end of orange 
 
 -,., ' JD 
 
 history j g 
 
 injury, nature and extent g 
 
 larva, first-stage, description 10-11 
 
 habit8 :..""!!";;;""";;!; 23-26 
 
 moltm g :.. 25-26 
 
 second-stage, description j j 
 
 larval period, length at Compton, Cal 32-34 
 
 in Imperial Valley 38 
 
 taping f ""i 
 
 length of life in winter 22-23 
 
 normal 
 
 life cycle, total length at Compton, Cal .,,, 35 
 
 mating, method j 7 _ lg 
 
 molting of larva 25-26 
 
 nymph, full grown. (See Thrips, bean, pupa.) 
 young. (See Thrips, bean, prepupa.) 
 
 occurrence, notes 40 
 
 ori g in '- ......'..'. 14-16 
 
 oviposition, method and time 18-19 
 
 number of eggs deposited 19-20 
 
 period 1 9_20 
 
 prepupa, description 12 
 
 habits 20-27 
 
 prepupal period, length at Compton, Cal 34-35 
 
 in Imperial Valley 38-39 
 
 pupa, description 13 
 
 habits 26-27 
 
 pupal period, length at Compton, Cal 34-35 
 
 in Imperial Valley 38-39 
 
 recent records 16-17 
 
 reproduction, kinds 20 
 
 seasonal history at Compton, Cal 31-37 
 
 Tempe, Ariz 39 
 
 in Imperial Valley 37-39 
 
 sexes, proportion 20 
 
 greenhouse. (See Heliothrips haemorrhoids!.*. > 
 
 pear, destructiveness in California 7 
 
 Tobacco extract, blackleaf, and whale-oil soap, against Heliothrips rubrodnctus 
 
 and bean thrips 44 
 
 Tomato, food plant of bean thrips 28 
 
 Triphleps insidiosus, enemy of bean thrips 42 
 
 Tropxolum major, food plant of bean thrips 31 
 
 Tulip poplar, bean thrips found thereon 31 
 
 Turnip, wild, food plant of bean thrips ' 31 
 
 Verbascum virgatum, food plant of bean thrips 31 
 
 Vetch, wild, food plant of bean thrips 31 
 
 Whale-oil soap. (See Soap, whale-oil.) 
 
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